CBSE Questions for Class 11 Engineering Chemistry States Of Matter Quiz 2 - MCQExams.com

Microscopic model of an ideal gas:

The model shows that the pressure that a gas exerts on the walls of its container is a consequence of the collisions of the gas molecules with the walls. 

• The number of molecules is large, and the average separation between molecules is great compared with their dimensions. This means that the volume of the molecules is negligible when compared with the volume of the container.
• The molecules obey Newtons laws of motion, but as a whole they move randomly. By randomly we mean that any molecule can move in any direction with equal probability. We also assume that the distribution of speeds does not change in time, despite the collisions between molecules. That is, at any given moment, a certain percentage of molecules move at high speeds, a certain percentage move at low speeds, and a certain percentage move at speeds intermediate between high and low.
• The molecules undergo elastic collisions with each other and with the walls of the container. Thus, in the collisions, both kinetic energy and momentum are constant.
• The forces between molecules are negligible except during a collision. The forces between molecules are short-range, so the molecules interact with each other only during collisions.
• The gas under consideration is a pure substance. That is, all of its molecules are identical.

Hint: Hydrogen bonding.

Explanation:

• Hydrogen bonding is a force of attraction between hydrogen and elements like $$N, O, F$$.
• There are two types of hydrogen bonding;

$$1.$$ Intramolecular hydrogen bonding: H-bonding within the molecule.
$$2.$$  Intermolecular hydrogen bonding: H-bonding between the two molecules.

$$ H-bonding\space between\space water\space and\space methanol$$

• The intermolecular H-bonding between the methanol and the water molecules is weaker than the intermolecular H-bonding among the water molecules.
• So, the vapor pressure of the aqueous solution of methanol is higher than the vapor pressure of pure water.

Hence, the correct answer is option $$C$$.

 Postulates of kinetic theory of gases:

1      The molecules in a gas are small and very far apart. Most of the volume which a gas occupies is empty space.
2      Gas molecules are in constant random motion. Just as many molecules are moving in one direction as in any other.

3      Molecules can collide with each other and with the walls of the container. Collisions with the walls account for the pressure of the gas.

4      When collisions occur, the molecules lose no kinetic energy; that is, the collisions are said to be perfectly elastic. The total kinetic energy of all the molecules remains constant unless there is some outside interference.

5      The molecules exert no attractive or repulsive forces on one another except during the process of collision. Between collisions, they move in straight lines. 

Hence options A,C & D are correct.

At any given temperature, the vapor pressure of a solution containing a nonvolatile solute is less than that of the pure solvent. This effect is called vapor pressure lowering. The solid line in Figure is a plot of the vapor pressure of pure water versus temperature. The break in the curve at 0°C is the intersection of the curve of the vapor pressure of the solid with the curve of the vapor pressure of the liquid. The dashed line in is a plot of the vapor pressure of an aqueous solution of sugar versus temperature. Notice that the vapor pressure of the solution is always less than that of the pure solvent. 

The surface of a pure solvent is populated only by solvent molecules. Some of these molecules are escaping from the surface, and others are returning to the liquid state. The surface of a solution is populated by two kinds of molecules; some are solvent molecules,