Question

Consider the mechanism. Step 1: A + B ⟶ C A+B⟶C slow Step 2: A + C ⟶ D A+C⟶D fast Overall: 2 A + B ⟶ D 2A+B⟶D Determine the rate law for the overall reaction, where the overall rate constant is represented as k .

Answer 1

Answer: The rate law expression for the overall reaction is $\text{Rate}=k[A]^2[B]$

Explanation:

Rate law is the expression that expresses the rate of the reaction in terms of the molar concentration of all the reactants each term raised to the power their stoichiometric coefficient in a balanced chemical equation.

In a mechanism of the reaction, the slow step in the mechanism determines the rate of the reaction.

For the given chemical reaction:  

$2A+B\rightarrow D$

The intermediate reaction of the mechanism follows:

Step 1:  $A+B\rightleftharpoons C;\text{ (slow)}$

Step 2:  $A+C\rightarrow D;\text{ (fast)}$

As, step 1 is the slow step. It is the rate determining step

Rate law for the reaction follows:

$\text{Rate}=k[A]^2[B]$

Hence, the rate law expression for the overall reaction is written above.