Question

The half life of a reaction is $46$ minutes when the initial concentration of the reactant is $0.4{\text{mol L}}^{-1}$ and $92$ minutes when the initial concentration is $0.2{\text{mol L}}^{-1}$. The order of the reaction is:

• A. $0$
• B. $0.5$
• C. $2$
• D. $1$

Answer 1

The correct option is C $2$

When the initial concentration is reduced from $0.4$ mol/L to $0.2$ mol/L, the half life period of the reaction increases from $46$ minutes to $92$ minutes.
Thus, when the initial concentration is reduced to half, the half life period doubles.
Hence, the half life period is inversely proportional to the initial concentration $(t_{1/2}\propto \frac{1}{a})$.
This is true only for the second order reaction.

Hence, the order of the reaction is $2$.