Question

Analyzing a new reaction

Consider the following elementary steps that make up the mechanism of a certain reaction:
3A→B+C
B+2D→C+F

1. What is the overall reaction?
2. What is the rate law for step one of this reaction?
3. What is the rate law for step two of this reaction?

Answer 1

(1) The overall reaction will be:

`3A+2D\rightarrow 2C+F`

(2) The rate law expression for the reaction is:

`\text{Rate}=k[A]^3`

(3) The rate law expression for the reaction is:

`\text{Rate}=k[B][D]^2`

Explanation :

Rate law : It is defined as the expression which expresses the rate of the reaction in terms of molar concentration of the reactants with each term raised to the power their stoichiometric coefficient of that reactant in the balanced chemical equation.

The general reaction is:

`A+B\rightarrow C+D`

The general rate law expression for the reaction is:

`\text{Rate}=k[A]^a[B]^b`

where,

a = order with respect to A

b = order with respect to B

R = rate law

k = rate constant

`[A]` and
`[B]` = concentration of A and B reactant

The given chemical equations are:

Step 1 :
`3A\rightarrow B+C`

Step 2 :
`B+2D\rightarrow C+F`

Part 1 :

Now we have to determine the overall reaction.

By adding both the reactions, we get:

`3A+B+2D\rightarrow B+C+C+F`

The overall reaction will be:

`3A+2D\rightarrow 2C+F`

Part 2 :

Now we have to determine the rate law for step one of this reaction.

Step 1 :
`3A\rightarrow B+C`

In this reaction, A is the reactant.

The rate law expression for the reaction is:

`\text{Rate}=k[A]^3`

Part 3 :

Now we have to determine the rate law for step two of this reaction.

Step 2 :
`B+2D\rightarrow C+F`

In this reaction, B and D are the reactants.

The rate law expression for the reaction is:

`\text{Rate}=k[B][D]^2`