# Organic Chemistry Questions and Answers – Reaction Kinetics

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Reaction Kinetics”.

1. For reaction system given below, volume is suddenly reduced to half of its value by increasing the pressure on it. If the reaction is of first order with respect to O2 and second order with respect to NO, what will be the change in the rate of reaction?
2NO(g) + O2(g) + 2NO2(g)
a) diminish to one-fourth of its initial value
b) diminish to one-eight of its initial value
c) increase to eight times of its initial value
d) increase to four times of its initial value

Explanation:

2. The rate law for a reaction between the substances A and B is given by rate = K[A]n [B]m. On doubling the concentration of A and halving the concentration of B. What will be the ratio of the new rate of the earlier rate of the reaction?
a) ($$\frac{1}{2}$$)m+n
b) m+n
c) n-m
d) 2n-m

Explanation:

3. Rate = If the volume of reaction vessel is suddenly reduced to $$\frac{1}{4}$$th of initial value. How new rate will be affected?
a) $$\frac{1}{10}$$
b) $$\frac{1}{8}$$
c) 8
d) 16

Explanation:

4. On which factor the rate constant of a reaction does not depend upon?
a) temperature
b) activation energy
c) catalyst
d) concentration of reactants and products

Explanation: The rate constant of reaction does not depend on concentration of reactant & product (only on nature of reactant & product).

5. The rate of reaction, A + B Products, is given by the equation, r = k[A][B]. If B is taken in excess, what would be the order of reaction?
a) 2
b) 1
c) zero
d) unpredictable

Explanation: A + B → Products
H = k[A][B] [if B is taken in large excess then according to pseudo first order reaction. B is taken as constant]. So, order = 1.

6. In a reaction, 2A2 + B2 → 2A2B, when the reactant A will disappear?
a) half the rate that B will decrease
b) the same rate that B will decrease
c) double the rate that A2B will form
d) twice the rate that B will decrease

Explanation:

So, the reactant A will disappear when A is twice the rate that B will decrease.

7. The rate of reaction that does not involve gases, is not dependent on _____________
a) pressure
b) temperature
c) concentration
d) catalyst

Explanation: The rate of reaction that does not involve gases does not depend on pressure.

8. Which is not true for a second order reduction?
a) It can have rate constant 1 x 10-2 L mol-1 s-1
b) Its half-life is inversely proportional to its initial concentration
c) Time to complete 75% reaction is twice of half-life
d) T50 = 1/(ka⋅A0)

Explanation:

but t75 = 3 * t50
So, option Time to complete 75% reaction is twice of half-life is wrong statement for n = 2.

9. The rate of decomposition of a substance increases concentration of substance at same temperature. Find out order of reaction.
a) 1
b) 2
c) 3
d) 0

Explanation: Rate = k [A]α
R1 = k[A]n
R2 = k [1.5 A]n = 2.25 R1
k(1.5A)n = 2.25*k*[A]n
(1.5)n * [A]n = 2.25*[A]n
n log (1.5) = log (2.25)
n = 2.

10. If a reaction is nth order the half-life period ________ of the initial concentration of the reactants.
a) is independent
b) varies inversely as (n-1)th power
c) varies inversely as nth power
d) varies directly as (n-1)th power

Explanation: For nth order; So, varies inversely as (n – 1)th power.

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