Question

In a reaction if the concentration of reactant $A$ is tripled, the rate of reaction becomes twenty seven times. What is the order of the reaction?

Answer 1

Explaining the rate law

The rate law is the expression in which the reaction rate is given in terms of the molar concentration of reactants, with each term raised to some power, which may or may not be equal to the stoichiometric coefficients of the reacting species, in a balanced chemical equation.

Let the reaction be,

$A\to B$

$rate=k[A{]}^m$

Where,

$k=$ rate constant

$m=$ order of reaction

Calculating the order of the reaction

If the concentration of reactant $A$ is tripled, the rate of reaction becomes twenty seven times (given).

Initially,

$rate=k[A{]}^m\dots ..(1)$

On tripling the concentration,

$rat{e}^{\prime }=27\times rate=k[3\times A{]}^m\dots \dots (2)$

Dividing equation $\left(2\right)$ by equation $\left(1\right)$

$\frac{27\times rate}{rate}=\frac{k[3\times A{]}^m}{k[A{]}^m}$

$27=3^m$

$m=3$

Hence, the order of reaction is $3.$