CBSE Questions for Class 12 Engineering Chemistry Chemical Kinetics Quiz 14 - MCQExams.com

For a reaction $$A \longrightarrow B+C$$ , it was found that at the end of 10 minutes from the start the total optical rotation of the system was $${ 50 }^{ o }$$ and when the reaction is complete, it was $${ 100}^{ o }$$. Assuming that only B and C are optically active and dextrorotatory. Calculate the rate constant of this first order reaction.
  • $$0.693 mi{ n }^{ -1 }$$
  • $$0.0693 se{ c }^{ -1 }$$
  • $$0.0693 { min }^{ -1 }$$
  • $$0.00693 { sec }^{ -1 }$$
The rate constant of a reaction at temperature 200 $$ \mathrm{K}  $$ is10 times less than the rate constant at 400 $$ \mathrm{K}  $$ . What is theactivation energy $$ \left(E_{\mathrm{a}}\right)  $$ of the reaction $$ (R= $$ gas constant)?
  • 1842.4$$ R $$
  • 921.2$$ R $$
  • 460.6$$ R $$
  • 230.3$$ R $$
for a zero order reaction-
  • $$t_{\frac{1}{2}}\propto  a$$
  • $$t_{\frac{1}{2}}\propto  \dfrac{1}{a}$$
  • $$t_{\frac{1}{2}}\propto  a^2$$
  • $$t_{\frac{1}{2}}\propto  \dfrac{1}{a^2}$$
For a first order reaction velocity constant is $$K={ 10 }^{ -3 }{ s }^{ -1 }$$,Two third life for it would be
  • 1100 s
  • 2200 s
  • 3300 s
  • 4400 s
Which one of the following formula represents a first-order reaction? 
  • $$K=\dfrac { x }{ t } $$
  • $$K=\dfrac { 1 }{ 2t } \left[ \dfrac { 1 }{ \left( 1-x \right) ^{ 2 } } -\dfrac { 1 }{ { a }^{ 2 } } \right] $$
  • $$K=\dfrac { 2.303 }{ t } { log }_{ 10 }\dfrac { a }{ \left( a-x \right) } $$
  • $$K=\dfrac { 1 }{ t } \dfrac { x }{ \left( a-x \right) } $$
A graph plotted between log $$t_{50\%}$$ vs log of concentration is a straight line. What conclusion can you draw from the given graph?
1531539_48c525fe24274fa7becfa7f4d6bc66c3.png
  • $$n=1,\ { t }_{ 1/2 }=\dfrac { 1 }{ k-a } $$
  • $$n=2,\ { t }_{ 1/2 }=1/a$$
  • $$n=1,\ { t }_{ 1/2 }= 0.693/k$$
  • none of these
Which of the following expression is correct for first- order  reaction? (CO) refers to initial concentration of reactant 
  • $${ t }_{ 1/2 }\propto CO$$
  • $${ t }_{ 1/2 }\propto { CO }^{ -1 }$$
  • $${ t }_{ 1/2 }\propto { CO }^{ -2 }$$
  • $${ t }_{ 1/2 }\propto { CO }^{ o }$$
For the first order reaction
    $${ 2N }_{ 2 }{ O }_{ 5 }\left( g \right) \longrightarrow { 4NO }_{ 2 }\left( g \right) +{ O }_{ 2 }\left( g \right) $$
  • the concentration of the reactant decrease exponentially with time
  • the half-life of the reaction decrease with increasing temperature.
  • the half-life of the reaction depends on the initial concentration of the reactant.
  • the reaction proceeds to 99.6% completion in eight half-life duration.
According to molecular collision theory, the reaction is subjected to:
  • Number of molecular collisions of reactant
  • Number of collisions between reactants and activated complex
  • The collision rate between reactants and product molecules
  • Number of effective molecular collisions of reactants
The reactions having very high values of energy of activation are generally________
  • Very slow
  • Very fast
  • Spontaneous
  • Medium fast.
Reaction $$A+B\rightarrow C+D$$ follows the following rate law:
$$Rate\ =k{ \left[ A \right]  }^{ 1/2 }{ \left[ B \right]  }^{ 1/2 }$$
 
On starting with initial conc. of 1 M of A and B each, what is the time taken for the concentration of A to becomes 0.25 M?
[Given;$$k=2.303\times { 10 }^{ -3 }{ sec }^{ -1 }$$]
  • 300 sec
  • 600 sec
  • 900 sec
  • None of these

The order of a reaction and rate constant for a chemical change having following curve would be:
1540669_6439cdd03d5944ee970c87d3d6a0998c.PNG
  • 0, 1/2
  • 1, 1
  • 2, 2
  • 0, 1
For a first order reaction, the value of rate constant for the reaction 

$$A_{(gas)}\longrightarrow 2B_{(gas)}+C_{(solid)}$$
  • $$\dfrac{1}{t}ln\left( \frac { { P }_{ 0 } }{ { P }_{ 0 }-{ P }_{ 1 } } \right) $$
  • $$\dfrac{1}{t}ln\left( \frac { { P }_{ 0 } }{ { 2P }_{ 0 }-{ P }_{ 1 } } \right) $$
  • $$\dfrac{1}{t}ln\left( \frac { { 2P }_{ 0 } }{ { 3P }_{ 0 }-{ P }_{ 1 } } \right) $$
  • $$\dfrac{1}{t}ln\left( \frac { { P }_{ 0 } }{ { 3P }_{ 0 }-{ P }_{ 1 } } \right) $$
From the above figure, the activation energy for the reverse reaction would be:
1537916_5aeb8895d0c8424cbc2cd23ac0bc8a3e.PNG
  • $$-120\  kJ{ mol }^{ -1 }$$
  • $$+152\  kJ{ mol }^{ -1 }$$
  • $$-120\  kJ{ mol }^{ -1 }$$
  • $$+1760\  kJ{ mol }^{ -1 }$$
The half life period for catalytic decomposition of $$  A B_{3}  $$ at $$ 50   \mathrm{mm}  $$ is found to be $$4 hrs$$ and at $$100 \mathrm{mm}  $$ it is $$2hrs$$. The order of reaction is -
  • $$3$$
  • $$1$$
  • $$2$$
  • $$0$$
For a zero order reaction $$ \mathrm{t}_{1 / 2} $$ is :
  • $$
    \frac{[\mathrm{A}]_{0}}{\mathrm{K}}
    $$
  • $$
    \frac{2[\mathrm{A}]_{0}}{\mathrm{K}}
    $$
  • $$
    \frac{[\mathrm{A}]_{0}}{2 \mathrm{K}}
    $$
  • $$
    \frac{1}{[\mathrm{A}]_{0} \mathrm{K}}
    $$
Which of the following represents threshold energy:
  • Activation energy + energy of the reactant
  • Activation energy - energy of the reactant
  • Activation energy
  • Energy of the reactants
Which of the following is correct with respect to a first order reaction?
  • A plot of rate and concentration is a positive straight line graph whose slope given the value of rate constant
  • A plot of log [A] and time is a straight line graph whose slope is $$-\cfrac { k }{ 2.303 } $$
  • A plot of log $$\cfrac { { [A] }_{ 0 } }{ [A] } $$ and time is a positive straight line graph whose slope is $$-\cfrac { k }{ 2.303 } $$
  • All of the above
For a given reaction of first order it takes 20 minutes for the concentration to drop from 1 M to 0.6 M. The time required for the concentration to drop from 0.6 M to 0.36 M will be:
  • More than 20 min
  • Less than 20 min
  • Equal to 20 min
  • Infinity
A reagent undergoes $$90  \% $$ decomposition in 366 min. according to the first-order reaction. Its half-life is :-
  • $$
    366 \times 100\left(\dfrac{\ln 2}{90}\right)
    $$
  • $$
    366\left(\dfrac{\ln 2}{\ln 10}\right)
    $$
  • $$
    \dfrac{1}{366}
    $$
  • 183
Which of the following graph(s) are correct for zero order reactions?
  • All of the above
The time taken for a first-order reaction to reduce the initial concentration by 4 times is 10 minutes. If the concentration is reduced 16 times, then the time required is:
  • 10 minutes
  • 96.33 minutes
  • 40 minutes
  • 80 minutes
Which among the following reaction is an example of a zero order reaction?
  • $$C_{12}H_{22}O_{11(aq)}+H_2O_{(l)}$$ $$\rightarrow C_6H_{12}O_{6(aq)}+C_6H_{12}O_{6(aq)}$$
  • $$2NH_{3(g)}\overset{Pt}{\rightarrow}N_{2(g)}+3H_{2(g)}$$
  • $$2H_2O_{2(l)}\rightarrow 2H_2O_{(l)}+O_{2(g)}$$
  • $$H_{2(g)}+I_{2(g)}\rightarrow 2HI_{(g)}$$
$$75\%$$ of a zero order reaction complete in 4 hr and  $$87.5\%$$ of the same reaction completes in 
  • $$6 h$$
  • $$4.64 h$$
  • $$8 h$$
  • $$2 h$$
Which option is valid for zero order reaction?
  • $$t_{1/2} = \dfrac {3}{2} t_{1/4}$$
  • $$t_{1/2} = \dfrac {4}{3} t_{1/4}$$
  • $$t_{1/2} = 2t_{1/4}$$
  • $$t_{1/4} = (t_{1/2})^{2}$$
The number of collisions of Ar atoms with the walls of container per unit time?
  • Increases when the temperature increases
  • Remains the same when $$CO_2$$ is added to the container at constant temperature
  • Increases when $$CO_2$$ is added to the container at constant temperature
  • Decreases, when the average kinetic energy per molecule is decreased
If X is the total number of collisions which a gas molecule registers with other molecules per unit time under particular conditions, then the collision frequency of the gas containing N molecules per unit volume is:
  • $$X/N$$
  • $$NX$$
  • $$2NX$$
  • $$NX/2$$
Consider the given plot of enthalpy of the following reaction between $$A$$ and $$B$$.
$$A + B\rightarrow C + D$$
Identify the incorrect statement.
1614270_baf9f19d9b8941c38163ad6bda5e6480.png
  • $$C$$ is the thermodynamically stable product
  • Formation of $$A$$ and $$B$$ from $$C$$ has highest enthalpy of activation
  • $$D$$ is kinetically stable product
  • Activation enthalpy of form $$C$$ is $$5\ kJ\ mol^{-1}$$ less than that to form $$D$$
The order of a reaction is zero. It will be definitely
  • exothermic
  • endothermic
  • elementary
  • complex
Which of the following is incorrect statement?
  • Stoichiometry of a reaction tells about the order of the elementary reactions
  • For a zero-order reaction, rate and the rate constant are identical
  • A zero-order reaction is controlled by factors other than the concentration of reactants
  • A zero-order reaction is always elementary reaction
Flask with greater mean free path for the molecules.($$r_{H_2}:r_{CH_4}:r_{O_2}=1:2:2$$)
  • A
  • B
  • C
  • Same for all
For a zero-order reaction,
  • the reaction rate is doubled when the initial concentration is doubled
  • the time for half change is half the time taken for completion of the reaction
  • the time for half change is independent of the initial concentration
  • the time for completion of the reaction is independent of the initial concentration
Flask with greater collision number of the molecules.
  • A
  • B
  • C
  • Same in all
Flask with greater number of collisions with the walls per unit area per unit time.
  • A
  • B
  • C
  • Same for all
When the temperature of an ideal gas is increased at constant pressure?
  • Collision number increases
  • Collision frequency increases
  • Mean free path increases
  • Number of molecules per unit volume increases
In a closed flask of $$5$$ litres $$1.0\ g$$ of $$H_2$$ is heated from $$300$$ to $$600\ K$$. Which statement is not correct?
  • Pressure of the gas increases
  • The rate of collisions increases
  • The number of moles of gas increases
  • The energy of gas molecules increases
One mole of helium and one mole of neon are taken in a vessel. Which of the following statements are correct?
  • Molecules of helium strike the wall of vessel more frequently
  • Moles of neon apply more average force per collision on the wall of vessel
  • Molecules of helium have greater average molecular speed
  • Helium exerts higher pressure than neon
A container (cylindrical, base area$$=821cm^2$$) fitted with frictionless, massless piston consists of five valves-I, II, III, IV, and V. The distance of valves from the initial position of the piston is $$15, 30, 40, 45$$ and $$50$$cm, respectively. The initial height of the piston from the base of the container was $$60$$cm. These valves open automatically if pressure exceeds over $$1.5, 2.2, 2.5, 4.4$$, and $$4.8$$ atm, respectively. Under the given conditions(shown in the diagram), the system is in a state of equilibrium. The piston is now compressed(moved downward) slowly and isothermally. Neglect the volumes of valve connectors. Select the correct option(s).
1680876_4acc57c1872d4eb1875629ad3dd550bd.png
  • Only the momentum of the molecules
  • Only the frequency of collision of molecules
  • Both momentum and frequency of collision of molecules
  • Neither momentum nor frequency of collision of molecules
The values of enthalpies of reactants and products are $$x$$ and $$y$$ $$J/mol$$, respectively. If the activation energy for the backward reaction is $$z$$ $$J/mol$$, then the activation energy for forward reaction will be
(in J/mol)
  • $$x-y-z$$
  • $$x-y+z$$
  • $$y-x-z$$
  • $$y-x+z$$
Hydrolysis of ethyl acetate is catalysed by $$HCl$$. The rate is proportional to the concentration of both the ester and $$HCl$$. The rate constant is $$0.1{ M }^{ -1 }{ h }^{ -1 }$$. What is the half-life, if the initial concentrations are $$0.02M$$ for the ester and $$0.01M$$ for the catalysing acid?
  • $$347h$$
  • $$519h$$
  • $$836h$$
  • $$693h$$
The initial rate of a zero-order reaction:
$$A(g)\rightarrow 2B(g)$$ is $$0.01M\quad { min }^{ -1 }$$. If the initial concentration of $$A$$ is $$0.1M$$, the concentration of $$B$$ after $$60s$$ is?
  • $$0.09M$$
  • $$0.01M$$
  • $$0.02M$$
  • $$1.2M$$
A zero-order reaction $$A\rightarrow B$$. At the end of $$1h$$, $$A$$ is $$75$$% reacted. How much of it will be left unreacted at the end of $$2h$$?
  • $$12.5$$%
  • $$6.25$$%
  • $$3.12$$%
  • $$0$$%
A first-order reaction: $$A(g)\rightarrow nB(g)$$ is started with $$A$$. The reaction takes place at constant temperature and pressure. If the initial pressure was $${P}_{0}$$ and the rate constant of reaction is $$K$$, then at any time, $$t$$ the total pressure of the reaction system will be
  • $${ P }_{ 0 }\left[ n+\left( 1-n \right) { e }^{ -kt } \right] $$
  • $${ P }_{ 0 }\left( 1-n \right) { e }^{ -kt }$$
  • $${ P }_{ 0 }.n{ e }^{ -kt }$$
  • $${ P }_{ 0 }\left[ n-(1-n) \right] { e }^{ -kt }\quad $$
For a zero-order reaction: $$2{ NH }_{ 3 }(g)\rightarrow { N }_{ 2 }(g)+3{ H }_{ 2 }(g)$$, the rate of reaction is $$0.1atm/s$$. Initially only $${ NH }_{ 3 }(g)$$ was present at $$3atm$$ and the reaction is performed at constant volume and temperature. The total pressure of gases after $$10s$$ from the start of reaction will be
  • $$4atm$$
  • $$5atm$$
  • $$3.5atm$$
  • $$4.5atm$$
The half-life periods of two first-order reactions are in the ratio $$3:2$$. If $${t}_{1}$$ is the time required for $$25$$% completion of the first reaction and $${t}_{2}$$ is the time required for $$75$$% completion of the second reaction, then the ratio, $${ t }_{ 1 }:{ t }_{ 2 }$$ is 
$$\left( \log { 3 } =0.48,\log { 2 } =0.3 \right) $$
  • $$3:10$$
  • $$12:25$$
  • $$3:5$$
  • $$3:2$$
At a certain temperature, the reaction between $$NO$$ and $${O}_{2}$$ is fast, while that between $$CO$$ and $${O}_{2}$$ is slow. It may be concluded that
  • $$NO$$ is more reactive than $$CO$$
  • $$CO$$ is smaller in size than $$NO$$
  • activation energy for the reaction:
    $$2NO+{ O }_{ 2 }\rightarrow 2{ NO }_{ 2 }$$ is less
  • activation energy for the reaction:
    $$2NO+{ O }_{ 2 }\rightarrow 2{ NO }_{ 2 }$$ is high
In general, the rate of a reaction can be increased by all the factors except
  • increasing the temperature
  • increasing the concentration of reactants
  • increasing the activation energy
  • using a catalyst
The time taken in $$75$$% completion of zero-order reaction is $$10h$$. In what time, the reaction will be $$90$$% completed?
  • $$12.0h$$
  • $$16.6h$$
  • $$10.0h$$
  • $$20.0h$$
The rate expression for a reaction is $$\cfrac { -dC }{ dt } =\cfrac { \alpha C }{ 1+\beta C } $$, where $$\alpha $$ and $$\beta$$ are constants and $$C$$ is the concentration of reactant at time, $$t$$. The half-life for this reaction is
  • $$\cfrac { 1 }{ \alpha } \ln { 2 } +\cfrac { \beta { C }_{ o } }{ 2\alpha } \quad $$
  • $$\cfrac { 1 }{ \beta } \ln { 2 } +\cfrac { \beta { C }_{ o } }{ 2\alpha } $$
  • $$\cfrac { \beta \ln { 2 } }{ \alpha } $$
  • $$\cfrac { \alpha }{ \beta } $$
Thermal decomposition of dibromosuccinic acid (DBSA) taking place according to the given equation, obeys first-order kinetics. The progress of reaction may be followed by means of alkali titration of the solution (definite volume of reaction mixture) at various time intervals. If $${T}_{0}$$ and $${T}_{t}$$ be the ml of alkali solution at zero time and at any time $$t$$, respectively and $$a$$ and $$(a-x)$$ be the concentrations of DBSA at zero time and at any time $$t$$, respectively, then the value of $$\cfrac { a }{ a-x } $$ is
  • $$\cfrac { { T }_{ o } }{ 3{ T }_{ 0 }-2{ T }_{ t } } $$
  • $$\cfrac { { T }_{ o } }{ { T }_{ t } } $$
  • $$\cfrac { { T }_{ o } }{ { T }_{ o }-{ T }_{ t } } $$
  • $$\cfrac { { T }_{ o } }{ { 2T }_{ o }-{ T }_{ t } } $$
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