Question

For a reaction $P\to Q$, the half-life of the reaction was 3h, when the initial concentration of P was 0.5M. As the concentration of P was increased to 1.0M, half life changes to 6h. The order of reaction with respect to P is:

• A. zero
• B. one
• C. two
• D. three

Answer 1

The correct option is A zero

We know the relation between half time and concentration i.e.

$t_{\frac{1}{2}}\propto \frac{1}{a^{(n-1)}}$ where $n$ is the order of reaction

$t_{\frac{1}{2}}=k\frac{1}{a^{(n-1)}}$

$(t_{\frac{1}{2}}{)}_1\times a_1^{(n-1)}=(t_{\frac{1}{2}}{)}_2\times a_2^{(n-1)}$

$3\times (0.5{)}^{n-1}=6(1{)}^{n-1}$

$(0.5{)}^{n-1}=2$

$2^{1-n}=2^1$

So comparing both the sides, we get

$1-n=1$

$n=0$

Hence, it is a zero-order reaction.