Chemical Kinetics - Order of Reaction and Reactants - Model Question

JEE Question 2007 Paper II

Consider a reaction aG+bH--> Products. When concentration of both the reactants G and H is doubled, the rate increases by eight times. However, when concentration of G is doubled keeping the concentration of H fixed, the rate is doubled. The overall order of the reaction is
(A) 0
(B) 1
(C) 2
(D) 3

Solution: D

This is a question of chapter chemical kinetics.
Reason: When G alone is doubled, rate is doubled. That is the exponent of [G] is one in rate law. When both are doubled, rate increases by 8 times, telling us that exponent of [H] is 2 in rate law. So overall order of reaction is sum of the two exponents that is 3.
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Chemical Kinetics - MCQ - One Answer only

1. The rate constant of a first order reaction depends on the

a. temperature
b. time
c. concentration of the reactant
d. concentration of the product
(JEE 1983)

Answer (a)

2. a catalyst is a substance which

a. increases the equilibrium concentration of the product
b. increases the equilibrium constant of the reaction.
c. supplies energy to the reaction
d. shortens the time to reach equilibrium
(JEE 1983)

Answer: (d)

Chemical Kinetics - True or False Type Questions

1. For a first order reaction, the rate of the reaction doubles as the concentration of the reactant(s) doubles. (1986)

Answer: True

Reason: For a first order reaction r = k[A].
Where r = rate of reaction
K = reaction constant
[A] = molar concentration of reactant
Hence if concentration doubles r also is doubled,.

2. Catalyst makes reaction more exothermic. (JEE 1987)

Ans: False
Catalyst does not affect the enthalpy of reaction. It affects only the rate of reaction.

Chemical Kinetics - Fill Blanks Type

1. The rate of chemical change is directly proportional to ______________. (JEE 1985)

Answer: concentration of reactants

2. In the Arrhenius equation, k = A exp(-E₀/RT), A may be termed as the rate constant at ____________ . (JEE 1997)

Answer: Very high temperature or zero activation energy.
As k becomes equal to A in either case.