Chapter U5.11, Problem 1E

Interpretation Introduction

Interpretation: The calculation of net energy exchange of a chemical reaction using average bond energies needs to be determined.

Concept introduction: In order to estimate the net energy of a chemical energy, we have to consider that a chemical reaction takes place in two parts which are energy needed in bond breaking and energy needed in bond making.

Answer to Problem 1E

The net energy exchange of a chemical reaction using average bond energies can be calculated as the sum of the total energy required in bond breaking and the bond making.

Explanation of Solution

In a chemical reaction the net exchange energy can be calculated as the sum of the energy input and the energy output.

For example, in the combustion of methane,

  ${\text{CH}}_{\text{4}}\text{+}{\text{2O}}_{\text{2}}\to {\text{CO}}_{\text{2}}\text{+}{\text{2H}}_{\text{2}}\text{O}$

The bond breaking total energy is 2642 kJ and the total net bond making energy is -3466 kJ.

Therefore, the total or the net energy can be calculated as,

  $\begin{array}{c}\text{Net}\text{energy}\text{exchange}\text{=}\left(\text{2642}\text{kJ}\right)\text{+}\left(-\text{3466}\text{kJ}\right)\\ =-824\text{kJ}\end{array}$

Conclusion

Bond energy can be used to calculate the net energy exchange of a chemical reaction.