Organic Chemistry Multiple Choice Questions 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
Answer: c
Clarification:
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
Answer: d
Clarification:
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
Answer: d
Clarification:
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
Answer: d
Clarification: 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
Answer: b
Clarification: 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
Answer: d
Clarification:
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
Answer: a
Clarification: 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)
Answer: c
Clarification:
but t75 = 3 * t50
So, option Time to complete 75% reaction is twice of half-life is wrong statement for n = 2.
