Question

Half-life period for decomposition of $N{H}_3$ over tungsten wire are given below:

Initial pressure in min	50	100	200
$t_{1/2}$	3.52	1.82	0.93

Order of the reaction is:

• A. II
• B. 0
• C. I
• D. None of these

Answer 1

Answer: (A)

II

The sum of powers of the concentration of the reactants in the rate law expression is called the order of that chemical reaction.

The half-life of a reaction is the time in which the concentration of a reactant is reduced to one-half of its initial concentration.

The half-life for a

zero order reaction is $t_{1/2}=\frac{\left[A_0\right]}{2k}$

first order reaction is $t_{1/2}=\frac{0.693}{k}$

second order reaction is $t_{1/2}=\frac{1}{k\times \left[A_0\right]}$

In the given table, half-life is decreasing on increasing the initial concentration. Only second-order reactions will have their half-life inversely proportional to initial concentration.

Therefore, above reaction is a second order reaction.