Question

Which among the following is a false statement?

• A. Rate of zero order reaction is independent of initial concentration of reactant.
• B. Half-life of a zero order reaction is inversely proportional to the rate constant.
• C. Molecularity of a reaction may be zero.
• D. For a first order reaction, \( t_{1/2} = 0.693/k \).

Hint:

Molecularity is always a positive integer, representing the number of molecules involved in an elementary reaction step.

Answer 1

The Correct Option is C

To solve the problem, we need to identify which among the given statements about reaction kinetics is false.

1. Analyzing Statement (A):
Rate of a zero-order reaction is independent of the initial concentration of reactant. For a zero-order reaction, the rate law is $ \text{Rate} = k $, which does not depend on concentration. This statement is true.

2. Analyzing Statement (B):
Half-life of a zero-order reaction is inversely proportional to the rate constant. The half-life for a zero-order reaction is given by $ t_{1/2} = \frac{[A]_0}{2k} $, where $ [A]_0 $ is the initial concentration. The half-life depends on $ [A]_0 $ and $ k $, but the statement claims it’s inversely proportional to the rate constant $ k $. Since $ t_{1/2} \propto \frac{1}{k} $, this statement is true.

3. Analyzing Statement (C):
Molecularity of a reaction may be zero. Molecularity represents the number of molecules colliding in an elementary reaction step and must be a positive integer (1, 2, or 3). It cannot be zero, as that would imply no molecules are involved, which is not possible for a reaction. This statement is false.

4. Analyzing Statement (D):
For a first-order reaction, $ t_{1/2} = 0.693/k $. For a first-order reaction, the half-life is $ t_{1/2} = \frac{\ln(2)}{k} \approx \frac{0.693}{k} $, which matches the given formula. This statement is true.

Final Answer:
The false statement is (C) Molecularity of a reaction may be zero.