Which of the following relation about first order and zero order reaction is correct?
Correct Answer :
Solution :
To determine the correct relationship between first-order and zero-order reactions, let us analyze the kinetics and timescales associated with each type of reaction.
First, let us look at a first-order reaction. The rate of a first-order reaction depends on the concentration of only one reactant.
The integrated rate equation for a first-order reaction is given by:
where is the initial concentration of the reactant, is the concentration of the reactant at time , and is the rate constant.
The half-life () is the time required for the reactant concentration to decrease to half of its initial value, meaning .
Substituting this into the first-order rate equation gives:
This shows that the half-life of a first-order reaction is a constant, independent of the initial concentration.
The time required for 100% completion of the reaction () corresponds to the concentration of reactant reaching zero ().
If we substitute into the integrated rate equation:
Because the term approaches infinity, a first-order reaction theoretically takes an infinite amount of time to reach 100% completion.
Therefore, we can state that:
For comparison, in a zero-order reaction, the rate is independent of the reactant concentration.
The integrated rate equation is:
The time for 100% completion () is a finite value:
While the half-life is:
Thus, for a zero-order reaction, the relationship is , which is not represented correctly in the incorrect options.
Hence, the correct statement is:
Access expert-curated educational resources and study materials—completely free.
Create, conduct, and manage professional online assessments with Mindyard. Perfect for teachers and institutes.
Copyright © 2026 Mindyard. All Rights Reserved.