Class 9 Chemistry - Matter In Our Surroundings

Explain why evaporation leads to cooling of the liquid?

When evaporation occurs liquid absorbs heat from the surroundings to get converted to its vapour form as a result, there is an overall decrease in the heat leading to cooling of the liquid.

What happens when we apply pressure to the particles of the matter?

Particles of matter will come nearer to each other and their Kinetic Energy additionally decreases.

Water kept in sunlight gets heat from the sun and is evaporated. But how does water kept under the shade of a tree also get evaporated? Explain.

Water gets evaporated despite being under the tree during the daytime because the air surrounding the tree also gets heated up from the presence of sunlight. So, water gets evaporated from the heated air.

Compare the three states of matter i.e. solids, liquids, and gases with reference to inter-particle space.

Inter-particle space is the space between the molecules or atoms. In solids, it is very less. In liquids, it is more than in solids but less than in gases. In gases, it's the maximum.

State some physical properties of matter.

$$\textbf{Physical Properties of Matter are:}$$
$$\text{Colour:}$$ Matter can be distinguished by their varied colours.
$$\text{Odour:}$$ Matter shows variation In odour or smell.
$$\text{Solubility:}$$ Matter may vary in solubility in water or other solvents.
$$\text{Melting & Boiling Points:}$$ Substances variation in their melting and boiling points.

Name the phenomenon which causes the following change:
Formation of water vapour from water.

The formation of water vapour from water is evaporation.

Evaporation is the phenomenon of the change of a liquid into vapours at any temperature below its boiling point.

Fill in the blanks:
Form of matter which has a definite volume but no definite shape is called a ___________.

Any matter which has a definite volume but no definite shape is called a liquid.

State if the following is a physical property of a substance.
Hydrogen sulphide gas has a strong rotten egg-like odour.

Odour is a physical property. So the smell of hydrogen sulphide like rotten eggs is a physical property.

Fill in the blank:
Liquids have a definite _______ .

In a liquid, the particles are still in close contact, so liquids have a definite $$volume$$.

Give scientific reasons.
A wet cloth is wrapped around water storage container in summer.

A wet cloth is wrapped around water containers in summers to keep the container and the water inside it cools. The water present in the cloth evaporates and along with that water, the heat also evaporates thus keeping the container and water cool.

How can we describe the movement of the molecules in the figure?

From the figure, we can see that the movement of molecules is possible in all directions because, in both images, there is enough space for the molecules to move around freely.

What produces more severe burns, boiling water or steam?

Give reason:

Icebergs float on ocean water.

Icebergs float in ocean water because the density of ice is less than water. The medium in which it floats but with most of the solid ice underwater.

When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the water slowly turns blue. Why?

When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the water slowly turns blue because of the diffusion of copper sulphate particles into water.

What is the evaporation what are the factors effecting it.

Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure.

Factors that affect evaporation include the concentration of the evaporating substances in air, temperature, pressure, rate of airflow, and surface area.

Give reason for the following.
We need to classify things.

We need to classify things in order to distinguish them. In this way, things can be categorized and can be easily studied.

Explain what you understand from the diagram.

Transitions between solid, liquid and gaseous phases involve a specific amount of latent heat absorbed or released.

If heat is added at a constant rate to mass of a solid, like ice, to change it to liquid water, it is called latent heat of fusion. The heat required to convert liquid to gas is latent heat of vaporization.

In the phase change from gas to liquid, there is a release of latent heat of condensation. Phase change from liquid to solid releases latent heat of solidification.

Why steam is used to run machines?

Since steam possesses a high amount of latent heat, it is able to provide more mechanical energy to run machines like steam engines, turbines etc.

The molecules in solids and liquids are in contact with each other. Explain.

Due to strong attraction forces, molecules in solids and liquids are in contact with each other but in gas, they are not in contact.

Define evaporation.

Evaporation, the process by which an element or compound transitions from its liquid state to its gaseous state below the temperature at which it boils

Why does a desert cooler cools better on a hot dry day?

The water when evaporated from a desert cooler absorbs energy from the surroundings and makes the surroundings cool. Evaporation is inversely proportional to humidity. Lesser the humidity and higher the temperature, the faster is the evaporation. So on a hot dry day, the humidity is less. Thus water present inside the desert cooler evaporates more, thereby cooling the surroundings more. That is why a desert cooler cools better on a hot dry day.

Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

What type of clothes should we wear in summer?

We should wear cotton clothes and light coloured clothes in summers. We sweat a lot in summers. Cotton is a good absorber of water. Thus, it absorbs sweat from our body and exposes the sweat to the atmosphere, making its evaporation faster. Further, light coloured clothes are poor absorbers of heat and would be better for summer.

For any substance, why does the temperature remain constant during the change of state?

Hint: The heat supplied to a system is used to break its intermolecular force of attraction.

Explanation:

The kinetic energy of particles in a substance is directly proportional to the temperature.

The relation is shown as;
$$K.E = \dfrac {3} {2}kT$$
Where $$K.E$$ = Kinetic energy
$$k$$ = Energy constant
$$T$$ = Temperature

As temperature increases the kinetic energy of particles also increases but in case of a change of state, the energy supplied to the substance by increasing temperature is used to break the intermolecular forces between the particles so that the state can be changed.

Hence, the temperature remains constant as all the heat is used up and no external heat is released or absorbed.

How does the water kept in an earthen pot (matka) become cool during summer?

$$Explanation:$$

Earthen pot (matka) has number of pores on its surface. From this pores, water from inside comes to outer side. Where water gains large surface area. Large surface increases the rate of evaporation of water.

Evaporation is a process in which water molecules from surface takes heat from water and converts into a gas state.

Due to loss of this, water and matka losses their heat and becomes cooler.

Due to this water kept in earthen pot (matka) become cooler during summer.

Arrange the following substances in increasing order of forces of attraction between the particles:
water, sugar, oxygen.

The increasing order of forces of attraction between the particles is as follows:

$$Oxygen < Water < Sugar$$

Sugar is solid. In solid, particles are very closer to each other so forces of attraction between the particles are also more.

Water is liquid. In liquid, particles are less closer than solid, so forces of attraction between the water particles also less than sugar.

Oxygen is gas. In gas, particles are very far from each other, so forces of attraction between the oxygen particles is very few.

What is the physical state of water at:
a. $$250^oC$$
b. $$100^oC$$

a. $$250^\circ C$$ - The boiling point of water is $$100^\circ C$$. Above this temperature, water is converted into steam. Therefore, water will be in its gaseous state.

b. $$100^\circ C$$ - Water boils at $$100^\circ C$$. Water can exist in both liquids as well as gaseous states. Only after giving a sufficient amount of heat (Latent heat of vaporization), the water will convert into its vapour form.

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Hint: In Water the molecules are held by weak intermolecular forces of attraction.

Explanation of answer:

A diver can cut through water in a swimming pool. The property of matter observed are:

This shows that the particles of matter have spaces between them.
The intermolecular forces of attraction between liquid particles are not very strong, hence the diver's force is enough to overcome these forces.

What is the physical state of water at:
$$(a)$$ $$25^{\circ}C$$
$$(b)$$ $$0^{\circ}C$$
$$(c)$$ $$100^{\circ}C$$

(a) The physical state of water at $$25^{\circ}C$$ is liquid.

(b) The physical state of water at $$0^{\circ}C$$ can be solid/liquid or both.

Boiling water and steam both have the same temperature $$(100^0C)$$, but steam causes many severe burns than boiling water. Explain

Water starts boiling at $$100^oC$$ and converts to steam. At the boiling temperature, particles of the steam have more energy than the particles of boiling water as they have absorbed extra energy in the form of latent heat of vaporization. So, particles of steam cause severe burns.

(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following:
Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

S.No	Property	Solid	Liquid	Gases
1.	Shape	They have a definite shape	They do not have a definite shape	They do not have a definite shape
2.	Volume	They have a definite volume	They do not have a definite volume	They do not have a definite volume
3.	Density	They have high-density	Liquids have less density than solids	Gases have the least density
4.	The kinetic energy of particles	Least	More than solids	Maximum
5.	Compressibility	Negligible	Low	High

Rigidity: It is the property of matter to resist the change of its shape.

Compressibility: It is the property of matter in which its volume is decreased by applying force.

Fluidity: Matter can flow.

Filling a gas container: On filling, a gas takes the shape of the container.

Shape: Having definite boundaries.

Kinetic energy: It is the energy possessed by the particles of matter due to its motion.

Density: It is the ratio of mass per unit volume

Why is ice at $$273\ K$$ more effective in cooling than water at the same temperature?

Cooling takes place when heat is removed. In the case of ice at $$273 K$$ ($$0^0C$$), it will first take the heat (the latent heat of melting) to convert itself into the water at $$273 K$$ Whereas, water at $$273 K$$ will absorb heat lesser than the latent heat of melting of ice and also its phase won't change until the temperature reaches $$373K$$ ($$100^0C$$).

So, at the same temperature of $$273 K$$, a large amount of heat will be removed by ice from the surroundings than in the case of water. Hence, ice at $$273 K$$ is more effective in cooling than water at the same temperature.

When water is boiled to $$100^oC$$, it converts into steam which on condensation gives back-water. Here, the heat given out is called ___________________ which is equal to the latent heat of vaporization.

The heat released is the latent heat of condensation.

Latent heat of condensation is the heat energy released when water vapor condenses to form liquid droplets. The same amount of energy is released in this process which was needed in the evaporation process.

How do you appreciate sweating mechanism of human body to control the temperature of the body?

In hot summer days, When sweat from our body evaporates, it absorbs energy from our body and makes our body cool. Thus, it decreases our body temperature.

Thus sweating mechanism of human body is important to keep our body cool in summers and also when temperature of our body rises.

A swimmer coming out of a pool is covered with a film of water weighing about $$80g$$. How much heat must be supplied to evaporate this water?

Latent heat of vaporization is defined as the amount of energy required to change state from liquid to vapor state.

Latent heat of vapourisation of water$$=540 \ cal/g$$

For $$80\ g$$ energy required is $$540\times 80 =43200\ cal =43.2\ kcal$$

The inter particle spaces are in gaseous and _ in solids.

The inter particle spaces are more in gaseous and less in solids.

Explain why dogs pant during hot summer days using the concept of evaporation?

Dogs, unlike humans do not have sweat glands or any other mechanisms to reduce the body temperatures. Therefore, we can often see dogs panting during the hot sunny days to reduce their body temperature using fundamental process called evaporation.

What is meant by intermolecular interaction ? What is its role in the states of matter ?

Definition:- Interactions between the constituent particles is called intermolecular interactions.

Role of Intermolecular Interaction:-

Intermolecular Interaction tells us the force of attraction present between the particles of different states such as solid, liquid, or gas. For eg:- Intermolecular interaction in solids is very tight or strong due to which they are hard and similarly intermolecular interactions tell us about the nature of the liquid and gaseous states.

State the appropriate scientific reasons for the following statement:
The rate of evaporation decreases with increase in humidity.

When humidity is high, the air is already saturated with water vapour. Therefore, it will not take more water vapour easily. Hence, rate of evaporation decreases.

What is evaporation? Explain four factors which affect the rate of evaporation.

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase.

The rate of evaporation is affected by,

(1) Temperature: Evaporation increases with an increase in temperature.

(2) Surface Area: Evaporation increases with an increase in surface area.

(3) Humidity: Evaporation decreases with an increase in humidity.

(4) Wind speed: Evaporation increases with wind speed.

Define the latent heat of fusion.

Latent heat of fusion is defined as the amount of heat energy required to change 1 kg of solid into liquid at its melting point. It is the energy, typically heat, provided to a substance to change its state from a solid to a liquid.

Can matter change its state?

Yes, matter can change its states between solid, liquid and gas.

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List down the characteristics of particles of matter.

Four main characteristics of particles of matter are:

Particles of matter are very tiny in size
They have spaces between them
Particles of matter move constantly
They are attracted to each other

Write the characteristic property of matter responsible for:
(a) Smell of perfume spreads in the room.
(b) Water takes the shape of the container in which it is kept

(a) Characteristics of the particles of "continuous movement" is responsible for the smell of perfume that spreads.

(b) Because of the loose interactions of the particles, the particles of liquid can move or flow and take the shape of the container in which they are kept.

For any substance, why does the temperature remain constant during the change of state?

When a substance is heated, the kinetic energy of the particles increases, and, as a result, temperature increases. But, during a change of state, the heat energy supplied to the substance is used to break the intermolecular forces between the particles so that the state can be changed. So, the temperature remains constant till a substance completely changes its state.

What are the factors affecting evaporation?

Factors affecting rate of evaporation are:

Surface area: Greater the surface area, higher will be the rate of evaporation and vice versa.
Temperature : Higher the temperature, higher will be the rate of evaporation and vice versa.
Humidity: Higher the humidity in the atmosphere, lesser will be the rate of evaporation and vice versa.
Wind speed: Higher the wind speed, higher will be the rate of evaporation.

Name two gases which are supplied in compressed form in homes and hospitals.

LPG (Liquefied Petroleum Gas) and oxygen gas are the two gases that are supplied in compressed form in houses and hospitals.

Liquefied Petroleum Gas (LPG) is a mixture of propane and butane and is used as a fuel at homes. Oxygen is used for artificial respiration in hospitals.

A manometer is connected to a gas containing bulb. The open arm reads $$43.7 \ cm$$ whereas the arm connected to the bulb reads $$15.6 \ cm$$. If the barometric pressure is $$743 \ mm$$ mercury. What is the pressure of gas in bar?

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Even two or three crystals of potassium permanganate can impart colour to a very large volume of water. Which characteristic of particles of matter is illustrated by this observation?

This observation displays that each crystal of Potassium Permanganate must be made up of millions of small particles i.e. particles of matter are very small.

Describe in your own words, what happens to the particles when salt dissolves in water.

When salt dissolves in water, the tiny salt particles occupy the spaces between the water particles. There won’t be any increase in volume of water.

A piece of chalk can be broken into small particles by hammering but a piece of iron cannot be broken into small particles by hammering. Which characteristic of the particles of matter is illustrated by these observations?

The matter is made up of small particles which attract each other and the attraction differs from substance to substance. Chalk breaks easily on hammering but iron cannot be broken which shows that the particles of iron attract each other with greater force.

Why do gases have neither fixed shape nor a fixed volume?

Gases do not have a fixed shape or volume so that the particles are freely moving. They do not have a fixed position or spaces between them.

Why can we easily move our hands in the air but do the same through a plank of wood, we need a karate expert? Explain.

There will be a weak force of attraction between the particles in the air. So we can move our hands-on air whereas the particles in solid plank are closely packed and a strong force of attraction exists between them. Hence it needs a huge force to overcome the attraction which a karate expert can do.

What do you think matter is made up of small particles or not ?

Yes, Matter is made up of small particles and these small particles are called Atoms. These atoms are basic building blocks of all types of matter.

What are the factors which affect the rate of evaporation ? Explain.

The factors which affect the rate of evaporation are:

(1) $$Surface area:$$
Evaporation is a surface phenomenon, As the surface area increases, more particles are present in the liquid surface area are exposed to the surroundings, and the rate of evaporation also increases.

(2) $$Tempearture:$$
With the increase in temperature, more particles are provided with kinetic energy to escape into the vapour state. Hence the rate of evaporation increases.

(3) $$Humidity:$$
Humidity is the amount of water vapour present in the air. For a given temperature, the air can only hold a particular amount of water vapour. So if the humidity is high, the amount of water vapour is high and hence the further conversion of a liquid into a vapour state is difficult or not favourable. Hence the rate of evaporation decreases.

(4) $$Wind$$ $$ Speed:$$
An increase in wind speed results in more moving away from water vapour particles with the wind, decreasing the amount of water vapour present in the air in that area. So the rate of evaporation increases with the wind speed.

How is a melting point related to intermolecular forces of attraction?

The minimum temperature at which solid melts to become a liquid at the atmospheric pressure is called its melting point.

When we increase the temperature of a solid substance the kinetic energy of the particles increases. Due to an increase in the kinetic energy of atoms or molecules starts vibrating with greater speed. The supplied heat energy overcomes the intermolecular forces of attraction between the molecules. At this temperature, molecules start moving more freely, and solid slowly convert to liquid.

Why water kept in an earthen pot during summers cools on its own?

An earthen pot contains tiny holes. The particles present don't the water surface take in heat from the surroundings and get converted into vapour. (The process involved is evaporation). The vapours escape through these tiny holes producing a cooling effect in the water inside the pot.

Why do people in villages use earthen pots in summer to cool water?

The temperature during summer is high which increases the rate of evaporation. Earthen pots are made of clay that have many minute pores in them. The pores increase the rate of evaporation of water as the water can move via the pores through capillary action. With the increase in the rate of evaporation, the heat energy leaves the pots in the form of kinetic energy of the evaporated water.

This, in turn, keeps the inside of the pot cool and the remaining water cooler. Hence, people in villages use earthen pots in summer to cool the water.

Conversion of ice into water and water into ice is an example of change that can be reversed. Give four more examples where you can say that the changes can be reversed.

Examples of reversible change
1) Inflating a balloon.
2) Melting of wax.
3) Folding of a paper.
4) Dissolution of sugar in water.

Paheli kept some water in a beaker for heating. She observed that tiny bubbles appeared before the water started to boil. She boiled the water for about $$5$$ minutes and filled it in a bottle up to the brim and kept the bottle air tight till it cooled down to room temperature. Why did the tiny bubbles appear?

The tiny bubbles upon heating water appeared because the dissolved air that is present in water started escaping, thus forming bubbles in the process.

Water can be made to boil even at a temperature below its normal boiling point $$(100^\circ C).$$ Explain.

The boiling of water does not only depend on temperature. Pressure also plays a role in the boiling of any liquid. When the pressure goes down below the atmospheric pressure of 1 atm, water starts to boil at a temperature lower than its boiling temperature.

Why do wet clothes placed on a clothes line get dry after some time? Explain.

Wet clothes placed on a clothesline get dry after some time because the water gets dried up from the heat of the sun. The water is converted into water vapour, the phenomenon is known as evaporation.

Give one example in each case.
Change which occurs on heating but can be reversed.

$$\text {Heating of an iron rod is a reversible change.}$$

If we heat an iron rod sufficiently it will get melted and if we stop heating and cool this iron rod, then it can get back to solid iron rod once again hence it is a reversible change.

A potter working on his wheel shaped a lump of clay into a pot. He then baked the pot in an oven. Do these two acts lead to the same kind of changes or not? Give your opinion and justify your answer.

These two actions lead to different kinds of changes.

1. When the lump of clay is shaped into a pot, only its physical properties are changed and chemically it remains clay.

2. When the pot is baked in the oven, its chemical properties are changed now we cannot get back the original clay using any physical process.

Show experimentally that matter is made up of small particles.

i) Take a $$100\,ml$$ beaker and fill it with $$50\,ml$$ water. Mark the level of water in the beaker.
ii) Add 1 tablespoon of salt to it.
iii) Stir the water until the salt crystals can no longer be seen and are completely dissolved. Note the level of water.
iv) The level of water does not increase.

Explanation: The level of water does not increase after the addition of salt. This observation supports the assumption that matter is made up of particles as a tablespoon of salt contains many salt crystals which are made up of salt crystals. These particles were able to dissociate in water and get evenly distributed in the intermolecular spaces present in water due to which the level of water did not change.

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Define Heat of Vaporization.

The quantity of heat required at a specified temperature to convert unit mass of liquid into vapor is called Heat of Vaporization.

State the three effects of heat on matter.

When a substance is heated, it can cause.
1. Interconversion of states of matter.
2. Thermal expansion of the substance.
3. It can also lead to the chemical change.

The behavior of matter in different states is governed by various physical laws. According to you, what are the factors that determine the state of matter?

Factors determining the state of matter are;

(I) Temperature

(ii) Pressure

(iii) Mass and Volume

Give reason:
Liquids have definite volume but no definite shape.

The molecules of the liquid are loosely packed and the intermolecular force of attraction is small but the number of molecules in it remains the same.

Hence, liquids have definite volume but no definite shape.

Give reason:
When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged.

When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged because the sugar particles are adjusted between the water molecules as inter-molecular gaps are more in liquids.

Give reason:
When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.

This is because gases can diffuse or flow in all directions.

At room temperature, the forces of attraction between the particles of solid substances are_________ than those which exist in the gaseous state.

At room temperature, the forces of attraction between the particles of solid substances are stronger than those which exist in the gaseous state.

Give reason:
A gas fills up the space available to it.

Gasses fill up the space available to them because gases don't have definite size, shape and boundary due to less attractive forces between particles. Random motion of their particles exerts pressure in all directions, and occupy any space available to them.

Conversion of solid state to liquid state is called fusion. What is meant by latent heat of fusion?

The amount of heat required to convert $$1$$ kg of any solid into liquid at its melting point at atmospheric pressure is known as the latent heat of fusion of that solid.

Give reason:
The odour of scent spreads in a room.

Molecules of the scent fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion. So, the odour of the scent spreads in the room.

Paheli kept some water in a beaker for heating. She observed that tiny bubbles appeared before the water started to boil. She boiled the water for about $$5$$ minutes and filled it in a bottle up to the brim and kept the bottle airtight till it cooled down to room temperature.
Do you think tiny bubbles will appear on heating the water taken out from the bottle? Justify your answer.

Paheli had boiled out the complete water that means all the air from the water escaped out, so boiling the water and later cooling it will not make tiny bubbles as there is no air present in it.

Fill in the blanks with the correct word/s from the bracket.
Matter can change from one state to another by change in ___________ [temperature or pressure, temperature only].
[Enter 1 if answer is temperature or pressure else 0 if temperature only]

Matter can change from one state to another by a change in $$\text {temperature or pressure}$$.

For example, a solid can change into a liquid with an increase in temperature of a substance or a liquid can change from a liquid state to a gaseous state with an increase in temperature.

Similarly, in the same manner, gases on compression can change to liquid.

Give a reason for the following.
Gases can be compressed easily.

The reason for this property of gases is that there is a very large intermolecular space between gas molecules. On mere applying pressure, they are easily compressed. Due to its high compressibility, a large amount of gas can be put in a small cylinder by compression.

Explain the term vaporization.

Matter can change from solid to liquid to gaseous state and back to solid state. This is called change of state of matter.

Vaporization - The process of conversion of a liquid into vapour on heating.

e.g. Water to water vapour.

Fill in the blank:
Liquids have no definite _______ .

Liquids have no definite shape. That's because the molecules in liquids have weak inter-particle forces of attraction compared to solids (that have definite shape).

Fill in the blanks with the correct word/s from the bracket.

The space between atoms in molecules of solids is ___________ [minimum / maximum].

The space between atoms in molecules of solids is $$\text {minimum}$$.

Inter-particle space is minimum in solid, it is moderate in liquid, and maximum in gases. Hence gaseous molecules are free to move anywhere.

Fill in the blank:
The temperature at which a liquid starts to boil is called the _______ point of that liquid.

The temperature at which a liquid starts to boil is called the boiling point of that liquid.

What was the ancient belief regarding the nature of matter?

The ancient belief about the nature of matter was that it is composed of four elements:

1. fire

2. air

3. wood

4. earth

Write your observation and conclusion for the following.
Ice is kept at room temperature.

When ice is kept at room temperature
$$\bullet \ \textbf{Observation:}$$ The ice melts and turns into liquid water.
$$\bullet \ \textbf{Conclusion:}$$ The room temperature is greater than the temperature of ice therefore, ice absorbs heat from the environment and melts to form liquid water.

What do you observe when a spoon of sugar is heated in a pan?

When a spoon of sugar is heated in a pan, black (Charred sugar or carbon) is formed. It's a chemical change.

Name a chemical change which takes place in presence of heat.

Burning of paper is an example of chemical change which takes place in presence of heat.

The burning of paper is a chemical change as paper after burning changes into ashes and fumes of gases evolved.

A change in which one or more new products are formed is called a chemical change.

Fill in the blanks:
The temperature at which a liquid starts changing into its vapour state is ______.

The temperature at which a liquid starts changing into its vapour state is $$\underline{\textbf{boiling point}}$$.
$$\underline{\textbf{For example}}$$- at a pressure of $$1$$ atm, the boiling point of water is $$100^\circ C$$ whereas the boiling point of ethanol is $$78.37^\circ C$$

A certain quantity of water is heated from 20$$ ^{\circ} $$C to 100$$ ^{\circ} $$C. Its temperature is recorded after each 1 minute. The observations are:
Time (in minute) Temperature ($$ ^{\circ} $$C)
0 20
1 30
2 40
3 50
4 60
5 70
6 80
7 90
8 100
9 100
10 100
11 100
12 100
What conclusion do you draw from the above table about the boiling point of water? Explain.

From the table given above, we note that as the thermometer shows 100°C, it becomes constant. This means the boiling point of water is 100°C and the heat supplied is being used to convert every molecule of water into vapors (steam) till the whole of the water gets boiled off.

Fill in the blanks .
The temperature at which a solid converts into a liquid is called its ________.

The temperature at which a solid is converted into liquid is called its melting point. For ice, the melting point is $$O^oC$$, from this temperature ice starts to melt and convert into water.

State three properties of molecules of a matter .

The properties of molecules of matter are listed below:

1. They are very small in size.
2. They have spaces between them.
3. They are in constant motion and possess kinetic energy.

Why does evaporation produce cooling?

Evaporation causes cooling because it requires heat energy. Heat energy is taken away by the particles of a liquid when they convert to vapour. As heat is taken away from the surroundings for evaporation, it causes cooling.

Why are volatile liquids such as alcohol and spirit stored in tightly closed bottles ?

Rate of evaporation depends on NATURE OF LIQUID .i.e more volatile liquid like ALCOHOL and SPIRIT evaporate easily, hence these are stored in tightly closed bottles to avoid their evaporation.

Wet clothes dry more quickly on a warm day than on a cold humid day. Explain

The rate of evaporation is directly proportional to temperature. Thus, the rate of evaporation is higher on warm days i.e hot days than on cold days having low temperatures and clothes dry soon on warm days.

Water in a dish evaporates faster than in a bottle. Give reason.

Rate of evaporation is more when the area of exposed surface is more. As area exposed in a dish is more, evaporation is also more.

Give reasons for the following.
Gases can be compressed easily.
Liquids can flow easily.
We need to classify things.
Pure substances have fixed melting or boiling points.
Electricity is not considered a matter.

1. Spaces between the molecules are large and, the interaction between the molecules is low in a gas, so it is easier to compress them by applying pressure.

2. In liquids, the Intermolecular force is weaker than that of solids. So molecules in a liquid can slip over one another and, liquids can flow, unlike solids.

3. We need to classify things to distinguish them. In this way, things can be categorized and can be easily studied.

4. Pure substances consist of only one kind of matter. All the particles of a pure substance are alike. It has a definite composition and similar properties. This is the reason that pure substances have fixed melting or boiling points.

5. Electricity neither has mass nor occupies space. Besides, it can not be seen by our eyes. This is why electricity is not considered a matter.

Fill in the blanks:
When a gas is cooled, its molecules _____ energy.

When a gas is cooled, its molecules lose energy, come closer to each other and eventually turn into their liquid form.

Fill in the blanks:
The temperature at which a liquid boils is called the ______ point of that liquid.

The temperature at which a liquid boils is called the boiling point of that liquid.

Fill in the blank:
Any matter which has a definite but no definite shape is called a .

Any matter which has a definite volume but no definite shape is called a liquid.

A liquid can change into a vapor state
(a) at a fixed temperature, and
(b) at all temperature
Name the process involved in two cases.

A liquid can change into a vapor state at a fixed temperature is known as boiling point.

A liquid can change into a vapor state at all temperatures is known as evaporation.

The process involved in the two cases is boiling or vaporization.

Some ice is taken in a beaker and its temperature is recorded after each one minute . The observation are listed below
from the above observation what conlusion do you draw about the melting point of ice ?

From the above observations we conclude that ice melts at $$0^{o}C$$ during which heart is supplied but the temperature does not rise shows that heat supplied is used to change every molecule of ice into water and when the whole of ice is melted, the temperature starts rising.

Doctors advise putting strips of wet cloth on the forehead of a person having a high fever. Why?

Heat is absorbed by water from its surroundings for phase change, from a liquid state to a gaseous state.

When strips of wet cloth are put on the forehead of a person having fever, the water in the cloth absorbs heat from the hot forehead to vaporise.

It helps to decrease the extra heat in the body caused due to high fever consequently helps to reduce body fever.

A certain quantity of water is heated from $$20^\circ C$$ to $$ 100^\circ C $$. Its temperature is recorded after each minute. The observations are:
Time in minutes Temperature ($$^\circ C$$)
0 20
1 30
2 40
3 50
4 60
5 70
6 80
7 90
8 100
9 100
10 100
11 100
What conclusion do you draw from the above table about the boiling point of water? Explain.

From the table given, we note that as thermometer reading reaches $$ 100^\circ C $$, it becomes constant though heat is continuously being supplied. This means boiling point of water is $$ 100^\circ C $$ and heat supplied after the boiling point is reached is being used to convert water (liquid) into vapours (steam) till whole of the water gets evaporated as steam. This supplied heat is called latent heat of vaporisation.

Explain the terms vaporization and boiling point .

VAPORIZATION: "Change of liquid to vapours (gas) on heating at constant temperature is called VAPORIZATION ."
When we heat a liquid temperature starts rising till it starts changing into vapours and then temperature remains constant for some time, though we are supplying heat. this heat supplied is being used to change every molecule of liquid into vapours and temperature does not rise till the whole of liquid is changed into vapours.
BOILING POINT: "The temperature at which a liquid starts changing into vapours or gas at constant temperature is called its BOILING POINT ".

Match the following .

Matter is made up of tiny particles called atoms or molecules.
At sea level, water boils at $$100^oC$$
At sea level, water freezes at $$)^oC$$
Evaporation is the process of changing liquid from vapour. Evaporation can take place at varying temperature.
Camphor is an example of sublimation process in which solid state converts to gaseous state.

Therefore correct options are
$$A \rightarrow 4, \ B \rightarrow 1, \ C \rightarrow 5,\ D \rightarrow 2, \ E \rightarrow 3$$

Explain why in hot summer day water remains cool in earthen pots.

Water seeps out through the pores in the earthen pot and it evaporates. The latent heat required for evaporation is taken, from water inside the pot which gets cooled.

Fill in the blanks
The smallest unit of matter that exists freely in nature is called a _________.

The smallest unit of matter that exists freely in nature is called a molecule.

Explain with an example to demonstrates that when a liquid evaporates, it takes heat from its surroundings.

If some spirit is poured on cotton wrapped around the bulb of a thermometer, the reading of the thermometer falls . This shows that cooling is produced when a liquid evaporates taking heat from surroundings.

Explain how the peculiar variation of density of water with temperature can
(a) protect marine-life
(b) cause water-pipes to burst in very cold places.

(a) Due to steep fall in the temperature in coastal regions, the density of water in the sea varies and the top layer of the seawater turns into ice and floats on the surface of sea-water because of lesser density than that of water whereas, the bottom denser layers of water remain, as usual, thus marine-life gets protected from freezing.

(b) The peculiar variation of density of water with temperature causes water pipes to burst in very cold places, it happens due to expansion of water on freezing. The water inside the pipes gets frozen and expands, pressing the inner walls of the water pipes, causing them to burst.

Identify A, B, C, and D; the first one is done for you.

A) Latent heat of fusion is the heat energy required to change a solid to liquid at atmospheric pressure and its melting point.

B) Latent heat of vaporisation is the heat energy required to change a liquid to gas at atmospheric pressure and its boiling point.

C) Latent heat of condensation is the heat energy released when a gas converts to liquid at atmospheric pressure and its boiling point.

D) Latent heat of solidification is the heat energy released when a liquid converts to solid at atmospheric pressure and its melting point.

Identify the state of a substance that has no shape and volume.

A gas has neither a definite volume nor shape. It is because the molecules in gases are very loosely packed, they have large intermolecular spaces and hence they move around. The force of attraction between molecules is also very less, as a result gases acquire any shape or any volume.

Why it is difficult to cook on hills compared to plains?

Water boils at a lower temperature on the hills, where the atmospheric pressure is lower than in the plains. This is why it takes longer time to cook in hilly regions.

Who am I ?
I make things hot or cold.

I am temperature because I am responsible for making things hot or cold.

Give reason:
On opening a bottle of a cold drink, a fizz sound is heard.

When the bottle is closed, the pressure inside the bottle is uniform, but as soon as the bottle is opened, there is a drastic change in the air pressure between the inside and outside of the bottle and the gas molecules suddenly have access to a lot more space to occupy. The result of this pressure difference is the ‘fizzzzz’ sound you hear when the bottle is uncapped; the trapped carbon dioxide molecules are escaping rapidly, so fast that you can hear it.

Give reason:
Carbonated drinks are bottled under high pressure.

Carbonated drinks are bottled under high pressure because the solubility of carbon dioxide increases with pressure.

How is molecular motion related with temperature?

Molecular motion is directly proportional to temperature. As the temperature increases, the kinetic energy of the molecules increases.

Butter and jelly both has the properties of solids and liquid explain.

When butter is kept at room temperature then it is in the solid-state but on heating, it changes into a liquid state.

Similarly, when the jelly is prepared, it is in a liquid state, but when it is frozen, it turns solid. Thus, they have the properties of both solids and liquids.

What are the states of matter on the basis of physical state?

On the basis of physical state matter is classified into three states — solid, liquid, and gas.

The matter which possess definite shape, mass and volume is called solid.

The matter which possess definite mass and volume but not definite shape is called liquid.

The matter which possess definite mass but indefinite volume and shape is called gas.

What do you observe?

We see that air takes the shape of the balloon. Now open the thread slowly, on opening the balloon air comes out to disappear in the atmosphere.

Steam has capacity to burn skin than boiled water at same temperature why?

Steam particles has more Kinetic energy.

What is the effect of pressure on density of liquid?

An increase in pressure increases the density of a liquid. When we increase the pressure on liquid the interparticle spacing decreases due to the that molecules become more closure to each other, in other words, volume decreases and density increases.

Define the latent heat of vaporisation.

Amount of heat energy required to change $$ 1 $$ kg of a liquid into a gas at atmospheric pressure at its boiling point is known as the latent heat of vaporisation of that liquid .

At room temperature, oxygen is a gas while water is a liquid. Why?

At room temperature oxygen is a gas while water is a liquid because the force of attraction present between the molecules of oxygen is weaker than the force of attraction present between the molecules of water.

Hence, the molecules of water are strongly bonded with each other at room temperature.

So, it is at a liquid state whereas the molecules of oxygen are not attached so strongly with each other and therefore, exist in the gaseous state.

Explain the effect of temperature on the state of matter.

If temperature increases or decreases, the state of matter gets changed to another state.

Example:

On heating ice (solid), it changes to water (liquid).

On cooling water (liquid) it again converted back to ice (solid).

What is the difference between boiling and evaporation?

* Evaporation occurs at the surface of the liquid whereas boiling occurs at the entire liquid.
* Evaporation occurs at any temperature whereas boiling occurs at a specific temperature.

What happens to the pressure when the volume is decreased?

Pressure is related to the number of particles in a given volume. More density

of the particles gives more pressure which means that particles present in a smaller volume will exert more pressure and vice versa. Hence, when the volume is decreased the pressure exerted by the particles will increase.

What happens on decreasing the pressure?

When pressure is decreased on a system volume increases.

When a gas is heated, the temperature is increased. What happens to the moment of molecules if the temperature of the gas is increased?

If the temperature of the gas is increased the Speed of motion increased

Considering the above diagram, is there any change in the number of molecules?

No there is no charge in the number of molecules

Define Temperature.

The average Kinetic energy of all the molecules in a substance its $$temperature.$$

What relation do you arrive at between pressure and volume of the gas?

As pressure increase volume decrease when pressure is reduced volume increased.

What changes can you observe in the volume of the gas inside the syring?

Volume is formed to be decreasing of the gas inside the syring.

As a result of increase in temperature, what happens to the energy of the particles?

When temperature is increased, the kinetic energy of the particles increases and they start vibrating with greater speed.

What is the difference between the notations $$l$$ and $$L$$ ?

'$$l$$' represents azimuthal quantum number which can have values $$ 0 , 1 , 2 $$ etc. L represents second Bohr orbit for which $$ n = 2 $$ always.

Write effect of pressure on state of matter.

The state of matter of a substance is attributed to the distance between the particles which make the substance. Thus, when pressure is applied on gas, it compresses to liquid and when pressure is increased on liquid, it becomes solid. The effect of pressure on solid is negligible.

Thus, if pressure is applied to a substance its state changes from:

Gas $$\to$$ Liquid $$\to$$ Solid.

The size of the air bubbles rising from the bottom of an aquarium increases. Can you explain the reason?

As the bubbles move upwards, the pressure on them decreases. This causes an increase in volume. So, as the bubbles move upwards, their size increases.

If a balloon is kept in sunlight, it will burst. What may be the reason for this?

When the balloon is placed in sunlight, the temperature increases, so the air volume inside the balloon increases. Thus balloon expands and finally bursts.

Write effect of temperature on state of matter.

When the temperature of a state of matter is increased, heat is absorbs by the substance in the form of energy. The kinetic energy of the molecules of the substance increase. The molecules experience a lot of vibration and occupy more space. As a result, a solid substance expands and becomes liquid and a liquid turns to gas.

Thus, on increasing the temperature of a substance, the following change in the states of matter is noted:

Solid $$\to$$ Liquid $$\to$$ Gas

Similarly, if the temperature of a substance is decreased:

Gas $$\to$$ Liquid $$\to$$ Solid.

Prabhu pushes an empty glass into a basin of water. The water is unable to enter the glass because air is occupying the space in the glass.
What can Prabhu do to allow the air to escape and the water to enter and take its place?

To allow the water into the glass, we have create an escape route for air, we can make a hole on top of glass which creates space for air to escape into the atmosphere and water to fill the glass.

In above tube is placed vertically with open end upward then find the length of the air column .

$$ P_1 = 75 \,cm $$ of $$ Hg , V_1 = 30 \times A $$

$$ P_2 = 75 + 10 + \dfrac{20.4 \times 10}{13.6} = 100 \,cm $$ of $$ Hg $$

$$ \Rightarrow $$ $$ 75 \times 24 = 100 \times x $$

$$ x = 18 \,cm $$

Give reason for the following.
A liquid generally flows easily.

A liquid generally flows easily because the intermolecular spaces between the liquid particles are more.

Moreover, these particles are loosely packed due to the presence of little force of attraction between them.

(a) Define matter. Give four examples of matter.
(b) What are the characteristics of matter ?

(a) Matter is anything that occupies and has mass. Wood, air, water, chalk, etc. are examples of matter.

(b) The characteristics of matter are:
1. Matter is made up of tiny particles.

2. Particles of matter attract each other.

3. Particles of matter have spaces between them.

4. Particles of matter are constantly moving.

Water is a matter because it has _ and occupies _.

Water is a matter because it has mass and occupies space.
Matter is anything which occupies space and has mass is called matter. Air and water, sugar and sand, hydrogen and oxygen etc.

When an incense stick (agarbatti) is lighted in one corner of a room, its fragrance spreads in the whole room quickly. Which characteristic of the particles of matter is illustrated by this observation?

This illustration shows that the particles are constantly moving in all directions.

Give two reasons to justify that:
(a) Water is a liquid at room temperature.
(b) An iron almirah is a solid.

(a) Water is a liquid at room temperature because

(i) Water has a fixed volume but no fixed shape.

(ii) Water flows freely.

(b) An iron almirah is solid because:

(i) The iron almirah has a fixed shape and volume.

(ii) Particles of the iron almirah do not flow freely and have a fixed position.

When a crystal of potassium permanganate is placed in a beaker, its purple color spreads throughout the water. What does this observation tell us about the nature of potassium permanganate and water?

The observation of purple color spreads throughout the water is that the crystal of potassium permanganate is made up of many small particles and these particles of potassium permanganate occupy the spaces between them.

How will you show that, by applying pressure, particles of matter can be brought close together?

Consider a cylinder containing a certain amount of gas. To apply pressure, the piston is lowered towards the gas particles as shown in the figure.

One can observe that as the applied pressure increases, the gas particles are forced to come closer and closer.

As a result, there is an increase in the intermolecular forces of attraction. Further increase in pressure would result in the liquefying of gas.

1625254_1771955_ans_83388ccef5934ea98584279c7945c557.png

When sugar is dissolved in water, there is no increase in the volume. Which characteristic of matter is illustrated by this observation?

The characteristic of matter illustrated by this observation is that the particles of water have spaces between them into which sugar particles fit.

The arrangement of particles is less ordered in the _ state. However, there is no order in the_ state.

The arrangement of particles is less ordered in the liquid state. However, there is no order in gaseous state. Because the force of attraction and particle distance are more in gaseous state than in liquid state.

Give reason:
A drop of ink added to water in a glass turns whole water blue.

$$\text{Solution}$$:

$$\bullet$$ When a drop of ink is added to water a homogeneous mixture of ink and water is formed. This solution appears uniform throughout and hence the whole water turns blue.
$$\bullet$$ Also, the liquid molecules are always in random motion, due to this, ink molecules move around the water and slowly mixes with water.

Write your observation and conclusion for the following:
When a small stone is gently dipped into a glass filled with water.

You will see that some water flows out of the tumbler and collects in the bowl. Remove the stone from the tumble. The level of water in the tumbler comes down. Now, pour the water collected in the bowl back into the tumbler. The glass tumbler is filled again. This is because the stone occupied space and therefore drives the water out of the tumbler. This proves that not only solids but liquids also occupy space.

Define solid, giving two examples.

A solid is that state of matter which has a fixed shape, mass, and volume. It shows very small changes in volume by changing the temperature. It can not be compressed,

e.g. — Sand, Wood, Copper, Ice, etc.

Give reasons for the following
Gas fills completely the vessel in which it is kept.

Gas fills completely the vessel in which it is kept because inter-particle attraction is weak and inter-particle space is large in gases which makes particles completely free to move randomly in the entire available space.

Describe a simple experiment to prove that solids occupy space.

Experiment:

$$A$$ - A measuring cylinder is filled with water to a particular mark - $$X$$.

$$B$$ - A piece of the wooden block is immersed inside the measuring cylinder. The water level rises up to $$C$$ - On removal of the block- the water level in the measuring cylinder falls down back to the mark $$X$$

Conclusion: The block pushes the water out and occupies its space, hence we can conclude that all solids occupy space.

1666091_1798983_ans_fa92855c1988429d838fec7e81054a32.png

Fill in the blank:
The substances which can flow are called _________.

The state of matter with definite volume and definite shape is called _______.

The state of matter with definite volume and definite shape is called $$\underline{\textbf{solid}}$$.
$$\bullet$$ The particles are tightly packed in solids.
$$\bullet$$ The intermolecular force of attraction is very strong and intermolecular space is almost negligible.

State the value of the ice point in terms of absolute temperature.

$$0^0C$$ is named as the ice point because water below this temperature exists as ice.

Ice point in terms of absolute temperature $$= 0^0C + 273 = 273 K$$

What do you conclude from the above experiment?

1. We conclude that wooden blocks and iron rods do no get compressed.
2. Solids have a definite shape and a definite volume.
3. The particles in solids are very close to each other.

Give reasons for the following :
The boiling point of a liquid rises on increasing pressure.

The energy required for the liquid molecules to expand to the gas phase increases as the pressure applied to the liquid surface increases, requiring a greater temperature to transform the liquid to gas phase. As a result, as pressure rises, the boiling point of a liquid rises.

Solid matter has the properties of definite shape and volume. Give reasons.

Solid matter has the properties of definite shape and volume because of the following reasons:

1) The inter-particle force of attraction between the particles of matter is very strong.
2) Inter-particle space between the particles of solid matter is negligible.
3) Particles of solid matter are very close to each other that they only vibrate at their fixed position.

Give reasons for the following:
Tea or coffee is sipped from the saucer when it is quite hot.

1928328_1865866_ans_66e6e3ac30174bbfb6388c0a5c4c906f.jpg

Time (in minute)	Temperature ($$ ^{\circ} $$C)
0	20
1	30
2	40
3	50
4	60
5	70
6	80
7	90
8	100
9	100
10	100
11	100
12	100

Time in minutes	Temperature ($$^\circ C$$)
0	20
1	30
2	40
3	50
4	60
5	70
6	80
7	90
8	100
9	100
10	100
11	100

Matter In Our Surroundings - Class 9 Chemistry - Extra Questions

Explain why evaporation leads to cooling of the liquid?

What happens when we apply pressure to the particles of the matter?

Water kept in sunlight gets heat from the sun and is evaporated. But how does water kept under the shade of a tree also get evaporated? Explain.

Compare the three states of matter i.e. solids, liquids, and gases with reference to inter-particle space.

State some physical properties of matter.

Name the phenomenon which causes the following change:Formation of water vapour from water.

Fill in the blanks:Form of matter which has a definite volume but no definite shape is called a ___________.

State if the following is a physical property of a substance. Hydrogen sulphide gas has a strong rotten egg-like odour.

Fill in the blank:Liquids have a definite _______ .

Give scientific reasons.A wet cloth is wrapped around water storage container in summer.

How can we describe the movement of the molecules in the figure?

What produces more severe burns, boiling water or steam?

Give reason: Icebergs float on ocean water.

When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the water slowly turns blue. Why?

What is the evaporation what are the factors effecting it.

Give reason for the following. We need to classify things.

Explain what you understand from the diagram.

Why steam is used to run machines?

The molecules in solids and liquids are in contact with each other. Explain.

Define evaporation.

Why does a desert cooler cools better on a hot dry day?

Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

What type of clothes should we wear in summer?

For any substance, why does the temperature remain constant during the change of state?

How does the water kept in an earthen pot (matka) become cool during summer?

Arrange the following substances in increasing order of forces of attraction between the particles: water, sugar, oxygen.

What is the physical state of water at:a. $$250^oC$$b. $$100^oC$$

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

What is the physical state of water at:$$(a)$$ $$25^{\circ}C$$$$(b)$$ $$0^{\circ}C$$$$(c)$$ $$100^{\circ}C$$

Boiling water and steam both have the same temperature $$(100^0C)$$, but steam causes many severe burns than boiling water. Explain

(a) Tabulate the differences in the characteristics of states of matter.(b) Comment upon the following: Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Why is ice at $$273\ K$$ more effective in cooling than water at the same temperature?

When water is boiled to $$100^oC$$, it converts into steam which on condensation gives back-water. Here, the heat given out is called ___________________ which is equal to the latent heat of vaporization.

How do you appreciate sweating mechanism of human body to control the temperature of the body?

A swimmer coming out of a pool is covered with a film of water weighing about $$80g$$. How much heat must be supplied to evaporate this water?

The inter particle spaces are __________ in gaseous and ___________ in solids.

Explain why dogs pant during hot summer days using the concept of evaporation?

What is meant by intermolecular interaction ? What is its role in the states of matter ?

State the appropriate scientific reasons for the following statement:The rate of evaporation decreases with increase in humidity.

What is evaporation? Explain four factors which affect the rate of evaporation.

Define the latent heat of fusion.

Can matter change its state?

List down the characteristics of particles of matter.

Write the characteristic property of matter responsible for:(a) Smell of perfume spreads in the room.(b) Water takes the shape of the container in which it is kept

For any substance, why does the temperature remain constant during the change of state?

What are the factors affecting evaporation?

Name two gases which are supplied in compressed form in homes and hospitals.

A manometer is connected to a gas containing bulb. The open arm reads $$43.7 \ cm$$ whereas the arm connected to the bulb reads $$15.6 \ cm$$. If the barometric pressure is $$743 \ mm$$ mercury. What is the pressure of gas in bar?

Even two or three crystals of potassium permanganate can impart colour to a very large volume of water. Which characteristic of particles of matter is illustrated by this observation?

Describe in your own words, what happens to the particles when salt dissolves in water.

A piece of chalk can be broken into small particles by hammering but a piece of iron cannot be broken into small particles by hammering. Which characteristic of the particles of matter is illustrated by these observations?

Why do gases have neither fixed shape nor a fixed volume?

Why can we easily move our hands in the air but do the same through a plank of wood, we need a karate expert? Explain.

What do you think matter is made up of small particles or not ?

What are the factors which affect the rate of evaporation ? Explain.

How is a melting point related to intermolecular forces of attraction?

Why water kept in an earthen pot during summers cools on its own?

Why do people in villages use earthen pots in summer to cool water?

Conversion of ice into water and water into ice is an example of change that can be reversed. Give four more examples where you can say that the changes can be reversed.

Water can be made to boil even at a temperature below its normal boiling point $$(100^\circ C).$$ Explain.

Why do wet clothes placed on a clothes line get dry after some time? Explain.

Give one example in each case.Change which occurs on heating but can be reversed.

A potter working on his wheel shaped a lump of clay into a pot. He then baked the pot in an oven. Do these two acts lead to the same kind of changes or not? Give your opinion and justify your answer.

Show experimentally that matter is made up of small particles.

Define Heat of Vaporization.

State the three effects of heat on matter.

The behavior of matter in different states is governed by various physical laws. According to you, what are the factors that determine the state of matter?

Give reason:Liquids have definite volume but no definite shape.

Give reason:When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged.

Give reason:When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.

At room temperature, the forces of attraction between the particles of solid substances are_________ than those which exist in the gaseous state.

Give reason:A gas fills up the space available to it.

Conversion of solid state to liquid state is called fusion. What is meant by latent heat of fusion?

Give reason:The odour of scent spreads in a room.

Fill in the blanks with the correct word/s from the bracket.Matter can change from one state to another by change in ___________ [temperature or pressure, temperature only].[Enter 1 if answer is temperature or pressure else 0 if temperature only]

Give a reason for the following. Gases can be compressed easily.

Explain the term vaporization.

Fill in the blank:Liquids have no definite _______ .

Fill in the blanks with the correct word/s from the bracket.The space between atoms in molecules of solids is ___________ [minimum / maximum].

Name the phenomenon which causes the following change:
Formation of water vapour from water.

Fill in the blanks:
Form of matter which has a definite volume but no definite shape is called a ___________.

State if the following is a physical property of a substance.
Hydrogen sulphide gas has a strong rotten egg-like odour.

Fill in the blank:
Liquids have a definite _______ .

Give scientific reasons.
A wet cloth is wrapped around water storage container in summer.

Give reason:

Icebergs float on ocean water.

Give reason for the following.
We need to classify things.

Arrange the following substances in increasing order of forces of attraction between the particles:
water, sugar, oxygen.

What is the physical state of water at:
a. $$250^oC$$
b. $$100^oC$$

What is the physical state of water at:
$$(a)$$ $$25^{\circ}C$$
$$(b)$$ $$0^{\circ}C$$
$$(c)$$ $$100^{\circ}C$$

(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following:
Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

The inter particle spaces are in gaseous and _ in solids.

State the appropriate scientific reasons for the following statement:
The rate of evaporation decreases with increase in humidity.

Write the characteristic property of matter responsible for:
(a) Smell of perfume spreads in the room.
(b) Water takes the shape of the container in which it is kept

Give one example in each case.
Change which occurs on heating but can be reversed.

Give reason:
Liquids have definite volume but no definite shape.

Give reason:
When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged.

Give reason:
When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.

Give reason:
A gas fills up the space available to it.

Give reason:
The odour of scent spreads in a room.

Fill in the blanks with the correct word/s from the bracket.
Matter can change from one state to another by change in ___________ [temperature or pressure, temperature only].
[Enter 1 if answer is temperature or pressure else 0 if temperature only]

Give a reason for the following.
Gases can be compressed easily.

Fill in the blank:
Liquids have no definite _______ .

Fill in the blanks with the correct word/s from the bracket.

The space between atoms in molecules of solids is ___________ [minimum / maximum].

Fill in the blank:
The temperature at which a liquid starts to boil is called the _______ point of that liquid.

Write your observation and conclusion for the following.
Ice is kept at room temperature.

Fill in the blanks:
The temperature at which a liquid starts changing into its vapour state is ______.

Fill in the blanks .
The temperature at which a solid converts into a liquid is called its ________.

Give reasons for the following.
Gases can be compressed easily.
Liquids can flow easily.
We need to classify things.
Pure substances have fixed melting or boiling points.
Electricity is not considered a matter.

Fill in the blanks:
When a gas is cooled, its molecules _____ energy.

Fill in the blanks:
The temperature at which a liquid boils is called the ______ point of that liquid.

Fill in the blank:
Any matter which has a definite but no definite shape is called a .

A liquid can change into a vapor state
(a) at a fixed temperature, and
(b) at all temperature
Name the process involved in two cases.

Some ice is taken in a beaker and its temperature is recorded after each one minute . The observation are listed below
from the above observation what conlusion do you draw about the melting point of ice ?

Fill in the blanks
The smallest unit of matter that exists freely in nature is called a _________.

Explain how the peculiar variation of density of water with temperature can
(a) protect marine-life
(b) cause water-pipes to burst in very cold places.

Who am I ?
I make things hot or cold.

Give reason:
On opening a bottle of a cold drink, a fizz sound is heard.

Give reason:
Carbonated drinks are bottled under high pressure.

Prabhu pushes an empty glass into a basin of water. The water is unable to enter the glass because air is occupying the space in the glass.
What can Prabhu do to allow the air to escape and the water to enter and take its place?

Give reason for the following.
A liquid generally flows easily.

(a) Define matter. Give four examples of matter.
(b) What are the characteristics of matter ?

Water is a matter because it has _ and occupies _.

Give two reasons to justify that:
(a) Water is a liquid at room temperature.
(b) An iron almirah is a solid.

The arrangement of particles is less ordered in the _ state. However, there is no order in the_ state.

Give reason:
A drop of ink added to water in a glass turns whole water blue.