Question

When initial concentration of a reactant is doubled in a reaction, its half-life period is not affected. The order of the reaction is:

• A. Zero
• B. First
• C. Second
• D. More than zero but less than first

Answer 1

The correct option is B

First

For a zero order reaction t_1/2 is directly proportional to the initial concentration of the reactant $\left[R_0\right]$
$t_{\frac{1}{2}}\propto \left[R_0\right]$
At $t_{\frac{1}{2}}\left[R\right]=\frac{\left[R_0\right]}{2}$
So, the above equation becomes
$K=\frac{2.303}{t_{\frac{1}{2}}}log\frac{\left[R_0\right]}{\frac{[R{]}_0}{2}}{t}_{\frac{1}{2}}=\frac{2.303}{K}=log2=\frac{2.303}{K}\times 0.3010t_{\frac{1}{2}}=\frac{693}{K}$
i.e., half life period is independent of initial concentration of a reactant.