chemistry - chemical kinetics

Class 12 - Chemistry

Chemical Kinetics

Q&A
Question:

Which of the following expressions is correct for the rate of reaction given below?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-13

Answer:

Rate law expression for the above equation can be written as
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-14
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-15

 



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Questions and Answers


Chemical Kinetics - Questions
1.

Mark the incorrect statements.
(a) Catalyst provides an alternative pathway to reaction mechanism.
(b) Catalyst raises the activation energy.
(c) Catalyst lower the activation energy.
(d) Catalyst alters enthapy change of the reaction.


Answer
2.

Write the rate equation for the reaction 2A + B–>C if the order of the
reaction is zero.


Answer
3.

In a reaction, if the concentration of reactant A is tripled, the rate of reaction becomes twenty-seven times. What is the order of the reaction?


Answer
4.

Oxygen is available in plenty in air yet fuels do not bum by themselves at room temperature. Explain.


Answer
5.

Match the items of Column I and Column II.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-45


Answer
6.

During decomposition of an activated complex
(a) energy is always released (b) energy is always absorbed
(c) energy does not change (d) reactions may be formed


Answer
7.

For a general reaction A –> B, plot of concentration of A versus time is
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-38
given in figure. Answer the following questions on the basis of this graph.
(i) What is the order of the reaction?
(ii) What is the slope of the curve?
(iii) What are the units of rate constant?


Answer
8.

Why does the rate of any reaction generally decreases during the course of the reaction?


Answer
9.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
(a) Both Assertion and Reason are correct and the reason is the correct explanation of Assertion.
(b) Both assertion and reason are correct but Reason is not the correct explanation of Assertion
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.
(e) Assertion is incorrect but Reason is correct.

The enthapy of reaction remains constant in the presence of a catalyst.
Reason (R): A catalyst participating in the reaction, forms different activated complex and lowers down the activation energy but the difference in energy of reactant and product remains the same.


Answer
10.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
(a) Both Assertion and Reason are correct and the reason is the correct explanation of Assertion.
(b) Both assertion and reason are correct but Reason is not the correct explanation of Assertion
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.
(e) Assertion is incorrect but Reason is correct.

Assertion (A): All collision of reactant molecules lead to product formation. Reason (R): Only those collisions in which molecules have correct orientation and sufficient kinetic energy lead to compound formation.


Answer
11.

Consider a first order gas phase decomposition reaction given below:
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-3


Answer
12.

Which of the following statement is not correct about order of a reaction?
(a) The order of a reaction can be a fractional number.
(b) Order of a reaction is experimentally determined quantity.
(c) The order of a reaction is always equal to the sum of the stoichiometric coefficients of reactants in the balanced chemical equation for a reaction.
(d) The order of a reaction is the sum of the powers of molar concentration of the reactants in the rate law expression.


Answer
13.

In any uni molecular reaction,
(a) only one reacting species is involved in the rate determining step
(b) the order and the molecularity of slowest step are equal to one
(c) the molecularity of the reaction is one and order is zero
(d) both molecularity and order of the reaction


Answer
14.

State a condition under which a biomolecular reaction is kinetically first order reaction.


Answer
15.

All energetically effective collisions do not result in a chemical change. Explain with the help of an example.


Answer
16.

Describe how does the enthalpy of reaction remain unchanged when a catalyst is used in the reaction?


Answer
17.

Activation energy of a chemical reaction can be determined by
(a) determining the rate constant at standard temperature
(b) determining the rate constants at two temperatures
(c) determining probability of collision
(d) using catalyst
(b) Activation energy of a chemical reaction is related to rate constant of a reaction at two different temperatures i.e.,K1 and  K2    respectively.


Answer
18.

Which of the following graph represents exothermic reaction?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-16


Answer
19.

The value of rate constant of a pseudo first order reaction
(a) depends on the concentration of reactants present in small amount
(b) depends on the concentration of reactants present in excess
(c) is independent of the concentration of reactants
(d) depends only on temperature


Answer
20.

Which of the following graphs are correct for a first order reaction?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-31
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-32


Answer
21.

Why is the probability of reaction with molecularity higher than three very rare?


Answer
22.

Why, in the redox titration of KMnO4versus oxalic acid we heat oxalic acid solution before starting the titration.


Answer
23.

Match the graph given in Column I with the order of reaction given in Column II. More than one item in Column I may link to the same item of Column II.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-42


Answer
24.

With the help of an example explain what is meant by pseudo first order reaction?


Answer
25.

The role of a catalyst is to change
(a) Gibbs energy of reaction (b) enthapy of reaction
(c) activation energy of reaction (d) equilibrium constant


Answer
26.

A graph of volume of hydrogen released vs time for the reaction between zinc and dil. HCl is shown below. On the basis of this, mark the correct option.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-9


Answer
27.

Rate law for the reaction ‘B' is doubled, keeping the concentration of ‘A'
constant, the value of rate constant will be
(a) the same (b) doubled (c) quadrupled (d) halved


Answer
28.

How can you determine the rate law of the following reaction?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-34


Answer
29.

Derive an expression to calculate time required for completion of zero order reaction. ‘


Answer
30.

The reaction between H2(g) and O2(g) is highly feasible yet allowing the gases to stand at room temperature in the same vessel does not lead to the formation of water. Explain.


Answer
31.

Why can we not determine the order of reaction by taking into consideration the balanced chemical equation?


Answer
32.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
(a) Both Assertion and Reason are correct and the reason is the correct explanation of Assertion.
(b) Both assertion and reason are correct but Reason is not the correct explanation of Assertion
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.
(e) Assertion is incorrect but Reason is correct.

Assertion (A): Order of the reaction can be zero or fractional.
Reason (R): We cannot determine order from balanced chemical equation.


Answer
33.

What happens to most probable kinetic energy and the energy of activation with increase in temperature?


Answer
34.

According to Arrhenius equation rate constant k is equal to  Ae-Ea/RT. Which of the following options represents the graph of In k versus ?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-6


Answer
35.

Which of the following expressions is correct for the rate of reaction given below?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-13


Answer
36.

Compounds ‘A' and ‘B' react according to the following chemical equation.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-18
Concentration of either ‘A' or ‘B' were changed keeping the concentrations of one of the reactants constant and rates were measured as a function of initial concentration. The following results were obtained. Choose the correct option for the rate equations for this reaction.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-19


Answer
37.

In the graph showing Maxwell Boltzmann distribution of energy,
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-27
(a) area under the curve must not change with increase in temperature
(b) area under the curve increases with increase in temperature
(c) area under the curve decreases with increase in temperature
(d) with increase in temperature curve broadens and shifts to the right hand side


Answer
38.

For a reaction A + B —> Products, the rate law is — Rate = k[A][B]3/2. Can – reaction be an elementary reaction? Explain.


Answer
39.

For a zero order reaction will the molecularity be equal to zero? Explain.


Answer
40.

Match the statements given in Column I and Column II.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-44


Answer
41.

Consider the following figure and mark the correct option.
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-2
(a) Activation energy of forward reaction is E1 + E2   and product is less stable than reactant.
(b) Activation energy of forward reaction is E1 + E2 and product is more stable than reactant.
(c) Activation energy of both forward and backward reactions is E1 + E2 and reactant is more stable than product.
(d) Activation energy of backward reaction is E, and product is more stable than reactant.


Answer
42.

Which of the following statement is correct?
(a) The rate of a reaction decreases with passage of time as the concentration of reactants decreases.
(b) The rate of a reaction is same at any time during the reaction.
(c) The rate of a reaction is independent of temperature change.
(d) The rate of a reaction decreases with increase in concentration of reactant(s).


Answer
43.

Rate law cannot be determined from balanced chemical equation if
(a) reverse reaction is involved
(b) it is an elementary reaction
(c) it is a sequence of elementary reactions
(d) any of the reactants is in excess


Answer
44.

According to Maxwell Boltzmann distribution of energy
(a) the fraction of molecules with most probable kinetic energy decreases at higher temperatures
(b) the fraction of molecules with most probable kinetic energy increases at higher temperatures
(c) most probable kinetic energy increases at higher temperatures
(d) most probable kinetic energy decreases at higher temperatures


Answer
45.

For a certain reaction, large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?


Answer
46.

Thermodynamic feasibility of the reaction alone cannot decide the rate of the reaction. Explain with the help of one example.


Answer
47.

Why cannot molecularity be applicable only for elementary reactions and order applicable for elementary as well as complex reaction?


Answer
48.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
(a) Both Assertion and Reason are correct and the reason is the correct explanation of Assertion.
(b) Both assertion and reason are correct but Reason is not the correct explanation of Assertion
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.
(e) Assertion is incorrect but Reason is correct.

Assertion (A): Order and molecularity are same.
Reason (R): Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of rate determining elementary step.


Answer
49.

In the presence of a catalyst, heat evolved or absorbed during reaction
(a) increases (b) decreases
(c) remains unchanged .(d) may increase or decrease


Answer
50.

Consider the reaction A —> B. The concentration of both the reactants and the products varies exponentially with time. Which of the following figures correctly describes the change in concentration of reactants and products with time?
ncert-exemplar-problems-class-12-chemistry-chemical-kinetics-21


Answer
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