Question

The time required for 100% completion of zero order reaction is:
A. $\dfrac{a}{k}$
B. $\dfrac{a}{2k}$
C. $\dfrac{2a}{k}$
D. $\dfrac{k}{a}$

Answer 1

Hint: Zero-order reaction is basically a reaction where the rate of reaction does not vary with the increase or decrease in the concentration of reactants. Hence, it is found that the rate of these reactions is always equal to the rate constant of the reactions.

Complete step by step solution:
- We will first write the kinetic equation of zero-order reaction as:
 x = kt
Where x is the amount of reactant converted into a product, k is the rate constant and t is time.
- If the initial concentration of reactants given is completely converted into a product, then we can say that it is 100% completion reaction.
- So, let us consider the initial concentration of reactant as a that is
     \[{{\left[ A \right]}_{\circ }}=a\]
- So, when the initial concentration of reactant forms amount of product equal to it then we will call it as the completed reaction,
- The value of x become a, means $a=k\times {{t}_{100}}$
Then, ${{t}_{100}}=\dfrac{a}{k}$
That is for a reaction to be 100% completed the time required is initial concentration upon ${{t}_{100}}=\dfrac{a}{k}$rate constant.

Hence, we can say that the correct option is (A), that is the time required for 100% completion of the zero-order reaction is $\dfrac{a}{k}$.

Note: - It is found that those reactions in which a catalyst is required are generally zero-order reactions.
- In a zero-order reaction, the unit of the rate constant is given by the ratio of concentration to time or we can say M/s, where s is second and M refers to molarity.