Question

The rate constant $k$ for the reaction shown is $1.63\times {{10}^{-6}}\text{ }{{M}^{-1}}\text{ }{{s}^{-1}}.$ What is the overall order of the reaction?
Reaction: $2IC{{l}_{\left( g \right)}}+{{H}_{2\left( g \right)}}\to 2HC{{l}_{\left( g \right)}}+{{I}_{2\left( g \right)}}.$
(A) $0$
(B) $1$
(C) $2$
(D) $3$

Answer 1

We know that the order of reaction is determined by experiment. Although if we know rate law expression determined experimentally then we can determine order of reaction using rate law. Order of reaction can be an integer or fractional value. Order of reaction can be zero and in zero order reaction the concentration of reactants doesn’t affect the rate of a reaction.

Complete answer:
As we know that the chemical reactions occur when two reactant molecules collide effectively, each having minimum energy and proper orientation. Reactant concentration, physical state of the reactants, surface area, temperature and the presence of a catalyst are some factors that affect reaction rate. The rate of reaction refers to the speed at which the products are formed from the reactants in a chemical reaction. It gives some insight into the time frame under which a reaction can be completed.
Thus, reaction kinetics is the study of the rate of chemical reactions, and reaction rates can vary greatly over a large range of time scales. The two main factors that affect the rate of a chemical reaction are the nature of reactants and surface area. Since reactant molecules exist in different phases in a heterogeneous mixture, the rate of reaction is limited by the contact surface area of the phases.
$K\propto \dfrac{1}{{{\left( C \right)}^{n-1}}}$ for n order of reaction which implies that the $K\propto \dfrac{1}{{{\left( m\times s \right)}^{2-1}}}$ where $n=2$ order of reaction.
On further solving we get; $K\propto \dfrac{1}{{{\left( m\times s \right)}^{+1}}}$
$\Rightarrow {{K}^{2}}{{m}^{-1}}{{s}^{-1}}$ which means that the order of reaction is second order reaction.
Therefore, the correct answer is option C.

Note:
Remember that the catalyst is a substance that accelerates a reaction by participating in it without being consumed and increases the rate of the reaction without actually participating in the reaction. It increases the speed of reaction in both forward and reverse reaction by following an alternate pathway which has lower activation energy.