CBSE Class 12 Chemistry Chemical Kinetics MCQs Set B

Question. The role of a catalyst is to change:
a. Gibbs energy of reaction
b. Enthalpy of reaction
c. Activation energy of reaction
d. Equilibrium constant

Answer: C

Question. Which of the following statements 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 rate law expression

Answer: C

Question. Which of the following statements 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: A

Question. Rate law for the reaction A + 2B → C is found to be Rate = k[A][B] Concentration of reactant ‘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: B

Question. Which of the following statements is incorrect about the collision theory of chemical reaction?
a. It considers reacting molecules or atoms to be hard spheres and ignores their structural features
b. Number of effective collisions determines the rate of reaction
c. Collision of atoms or molecules possessing sufficient threshold energy results into the product formation
d. Molecules should collide with sufficient threshold energy and proPER orientation for the collision to be effective

Answer: C

Question. In the presence of a catalyst, the heat evolved or absorbed during the reaction:
a. Increases
b. Decreases
c. Remains unchanged
d. May increase or decrease

Answer: C

Question. Activation energy of a chemical reaction can be determined by:
a. Determining the rate constant at standard temperature
b. Determining the rate constant at two temperatures
c. Determining probability of collision
d. Using catalyst

Answer: B

Question. Consider the Arrhenius equation given below and mark the correct option:k = Ae ^-Ea/RT
a. Rate constant increases exponentially with increasing activation energy and decreasing temperature
b. Rate constant decreases exponentially with increasing activation energy and decreasing temperature
c. Rate constant increases exponentially with decreasing activation energy and decreasing temperature
d. Rate constant increases exponentially with decreasing activation energy and increasing temperature

Answer: D

Question. A first order reaction is 50% completed in 1.26 × 10¹⁴ s. How much time would it take for 100% completion?
a. 1.26 ×10¹⁵ s
b. 2.52 × 10¹⁴ s
c. 2.52 × 10²⁸ s
d. Infinite

Answer: D

Question. Which of the following statement is not correct for the catalyst?
a. It catalyses the forward and backward reactions to the same extent
b. It alters ΔG of the reaction
c. It is a substance that does not change the equilibrium constant of a reaction
d. It provides an alternate mechanism by reducing activation energy between reactants and products

Answer: B

Question. The value of rate constant of a pseudo first order reaction:
a. Depends on the concentration of reactants presents 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: B

Question. 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: A, C, D

Question. During decomposition of an activated complex:
a. Energy is always released
b. Energy is always absorbed
c. Energy does not change
d. Reactants may be formed

Answer: A, D

Question. 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 increase at higher temperatures
c. Most probable kinetic energy increases at higher temperatures
d. Most probable kinetic energy decreases at higher temperatures

Answer: A, C

Question. In the graph showing Maxwell, Boltzmann distribution of energy:
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: A,D

Question. Which of the following statements are in accordance with the Arrhenius equation?
a. Rate of a reaction increases with increase in temperature
b. Rate of a reaction increases with decrease in activation energy
c. Rate constant decreases exponentially with increase in temperature
d. Rate of reaction decreases with decrease in activation energy

Answer: A, B

Question. Which of the following statements are applicable to a balanced chemical equation of an elementary reaction?
a. Order is same as molecularity
b. Order is less than the molecularity
c. Order is greater than the molecularity
d. Molecularity can never be zero

Answer: A, D

Question. In any unimolecular 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 are one

Answer: A, B

Question. For a complex reaction:
a. Order of overall complex reaction is same as molecularity of the slowest step
b. Order of overall reaction is less than the molecularity of the slowest step
c. Order of overall reaction is greater than molecularity of the slowest step
d. Molecularity of the slowest step is never zero or noninteger

Answer: A, D

Question. Mark the incorrect statements:
a. Catalyst provides an alternative pathway to reaction mechanism
b. Catalyst raises the activation energy
c. Catalyst lowers the activation energy
d. Catalyst alters enthalpy change of the reaction

Answer: A, D

Directions: These questions consist of two statements each, printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
A. If both Assertion and Reason are True and the Reason is a correct explanation of the Assertion.
B. If both Assertion and Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion and Reason are False.

Question. Assertion: The molecularity of the reaction H₂ + Br₂ → 2HBr is 2.
Reason: The order of this reaction is 3/2.

Answer: B

Question. Assertion: On addition of AgNO₃ to NaCl, precipitation occurs slowly.
Reason: The reaction is non-ionic.

Answer: B

Question. Assertion: For the first order reaction half-life period is expressed as t_1/2 = (2.303/K) log₁₀ 2
Reason: The half-life time of a first order reaction is not always constant and it depends upon the initial concentration of reactants.

Answer: C

Question. Assertion: In a multi step reaction, the molecularity of overall reaction has no significance.
Reason: Molecularity refers to the order of rate determining step.

Answer: C

Question. Assertion: For zero order reaction, the concentration vs time graph is a straight line.
Reason: The rate of change of concentration per unit time in zero order reaction remains constant.

Answer: A

Question. Assertion: Catalyst increases the rate of a reaction.
Reason: It lowers threshold energy of the reaction.

Answer: A

Question. Assertion: Fraction of total molecules having energy equal to or greater than activation energy K/A = e ^-Ea/RT
Reason: Activation energy of a chemical reaction is always constant at a given temperature.

Answer: C

Question. Assertion: Temperature coefficient of the different reaction lie between 2 to 3.
Reason: The rate of a reaction increase between 2 to 3 times by 10°C rise in temperature.

Answer: A

Question. Assertion: In effective collision, the energy of molecules can be greater than threshold energy.
Reason: In effective collisions, molecules do not have proper orientation.

Answer: C

Question. Assertion: The rate of the reaction is the rate of change of concentration of a reactant or a product.
Reason: Rate of reaction remains constant during the complete reaction.

Answer: C

Question. Assertion: If in a zero order reaction, the concentration of the reactant is doubled, the half-life period is also doubled.
Reason: For a zero order reaction, the rate of reaction is independent of initial concentration.

Answer: B

Question. Assertion: The order of the reaction CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH is 2.
Reason: The molecularity of this reaction is 2.

Answer: D

I. MCQ - Choose Appropriate Alternative

Question. The rate of chemical reaction __________ with increase in concentration of the reactants. (Increases, Decreases, Does not alter)

Question. Ionic reactions of inorganic compounds are __________. (very slow, moderately slow, very fast)

Question. The rate of __________ reactions can be determined. (Very Slow, Moderately Slow, Very fast)

Question. The sum of exponents of the concentrations of reactants is called __________. (Order of reaction, Molecularity, Equilibrium Constant)

Question. The rate of reaction generally __________ in the presence of a suitable catalyst.  (Increases, Decreases, remains constant)

Question. The rate of a reaction __________ upon the temperature. (depends, slightly depends, does not depends)

Question. The minimum energy required to bring about a chemical reaction is called __________. (Bond energy, Ionization energy, Energy of Activation)

Question. Oxidation of SO₂ in the presence of V₂O₅ in Sulphuric Acid industry is an example of __________. (Homogenous catalyst, Heterogeneous catalyst, Negative catalyst)

Question. Hydrolyses of ester in the presence of acid is an example of __________. (Homogenous catalyst, Heterogeneous catalyst, Negative catalyst)

Question. Concentration of the reactants __________ with the passage of time during a chemical reaction. (Increases, Decreases, Does not alter)

Question. Concentration of the products __________ with the passage of time during a chemical reaction. (Increases, Decreases, Does not alter)

Question. The rate constant __________ with temperature for a single reaction. (Varies, Slightly Varies, Does not vary)

Question. The rate of reaction at a particular time is called __________. (Average Rate of reaction, Absolute rate of reaction, Instantaneous rate of reaction)

Question. The specific rate constant K has __________ value for all concentrations of the reactant. (Fixed, Variable, negligible value)

Question. By increasing the surface area the rate of reaction can be __________. (Increased, Decreased, Doubled)

Question. MnO₂ when heated with KClO₃ __________. (Gives up its own oxygen, Produces ozone O₃, Acts as catalyst)

Question. Reactions with high energy of activation proceed with __________. (High speed, Moderately slow speed, slow speed)

Question. The minimum amount of energy required to bring about a chemical reaction is called __________. (Energy of ionization, Energy of Activation, Energy of Collision)

Question. An inhibitor is a catalyst which __________ rate of reaction. (Increases, Decreases, Does not alter)

Question. __________ is the change of the concentration of reactant divided by the time. (Rate of reaction, Velocity Constant, Molecularity)

II. Fill in the Blank

Question. The branch of chemistry, which deals with the study of rates and mechanisms of chemical reactions, is known as __________.

Question. Such reactions, which proceeds with very high velocities and are completed very quickly are called __________ reactions.

Question. Such reactions, which take place very slowly, are called __________ reactions.

Question. Reactions between silver nitrate and sodium chloride to form white precipitates of silver chloride are an example of __________ reaction.

Question. Reactions of Organic compounds are slow and are called __________ reactions.

Question. There are some reactions, which proceed slowly with a __________ speed.

Question. The rate of __________ reaction can only be determined.

Question. The amount of chemical change taking place in concentration of the per unit time is called __________ of reaction.

Question. Rate of reaction is expressed in __________.

Question. The rate of reaction between two specific interval of time is called __________.

Question. The addition energy required to bring about a chemical reaction is called __________.

Question. According to __________ theory for a chemical reaction to take place, the reacting molecules must come closed together.

Question. The addition of __________ helps the reaction by lowering the energy of activation.

Question. The rate of reaction __________ with the increase in concentration of the reacting molecules.

Question. When the concentration of both the reacting molecules is double, the probability of collisions between them will be __________ times.

Question. By __________ the surface area of the reactants, the rate of reaction is increased.

Question. Rate of reaction generally __________ with the rise of temperature.

Question. A __________ is a substance, which either accelerates or retards the rate of reaction without taking part in the reaction.

Question. In the preparation of Oxygen from Potassium Chlorate, __________ is used as catalyst.

Question. In the oxidation of SO₂ to SO₃ by the contact process for the manufacture of H₂SO₄ __________ is used as catalyst.

Question. An unstable intermediate compound formed during a chemical reaction is called __________.

Question. When a catalyst and the reactants are in the same phases, it is known as __________ catalyst.

Question. When a catalyst and the reactants are in different phases, it is called __________.

Question. When a catalyst increases the rate of reaction, it is called __________ catalyst.

Question. When a catalyst retards the rate of reaction, it is called __________ catalyst.

Question. A negative catalyst __________ the energy of activation, hence the rate of reaction is decreased.

Question. The ratio between the rate of reaction and concentration of reactants is known as __________.

Question. Velocity constant is independent of concentration but depends on __________.

Question. Ionic reactions are __________ than molecular reactions.

Question. The value of specific rates constant for a reaction __________ with time.