Chapter 18, Problem 85A

Interpretation Introduction

Interpretation: The activation energy of the reverse reaction is to be calculated.

Concept introduction: The term "activation energy" refers to the minimal amount of additional energy a reactive molecule needs to transform into a product during a chemical reaction.

Answer to Problem 85A

The activation energy of the reverse reaction is $\text{25 kJ}$ .

Explanation of Solution

The reversible reaction is as follows:

  $\text{A}+\text{B}\rightleftharpoons \text{C}$

The activation energy of the forward reaction is $5\text{ kJ}$ .

The total energy change is $-20\text{ kJ}$ .

The formula to calculate the total energy change is as follows:

  $\text{Total energy change}=\left(\begin{array}{c}\text{Activation energy of the forward reaction}\\ -\text{Activation energy of the reverse reaction}\end{array}\right)$

Substitute the value of activation energy of the forward reaction and total energy change in the above formula.

  $\begin{array}{c}\text{Total energy change}=\left(\begin{array}{c}\text{Activation energy of the forward reaction}\\ -\text{Activation energy of the reverse reaction}\end{array}\right)\\ -20\text{ kJ}=\left(\begin{array}{c}5\text{ kJ}\\ -\text{Activation energy of the reverse reaction}\end{array}\right)\\ \text{Activation energy of the reverse reaction}=\text{25 kJ}\end{array}$

Therefore, the activation energy of the reverse reaction is $\text{25 kJ}$ .

Conclusion

The activation energy of the reverse reaction is $\text{25 kJ}$ .