Chapter U5, Problem 13STP

Interpretation Introduction

Interpretation:

The total energy required to break all the bonds in 1 mole of ethanol needs to be determined.

Concept introduction:

The bond energy of a chemical bond can be defined as the energy required to break that chemical bond. The bond energy that is needed to break the bonds in reactant molecule and the energy released to form chemical bonds in product can be used to calculate the $\Delta \text{H}$ of the chemical reaction.

Thus, the sum of bond energies of all bonds in a molecule will be the energy which requires to break all bonds.

Answer to Problem 13STP

Option (C) is correct answer.

$\text{ΔH= 3240 kJ/mol}$

Explanation of Solution

Reason for correct option:

Structure of ethanol can be shown as:

Total energy required to break all bonds:

$\begin{array}{l}\text{ΔH=}1\times {\text{BE}}_{\text{C-C }}\text{+ }5\times {\text{BE}}_{\text{C-H }}\text{+ }1\times {\text{BE}}_{\text{C-O }}+{\text{1×BE}}_{\text{O-H}}\\ \text{ΔH=}1\times \text{347+ }5\times \text{413+ }1\times \text{358}+\text{1×467}\\ \text{ΔH= 3237 = 3240 kJ/mol}\end{array}$

Conclusion

Reasons for incorrect options: The sum of bond energies of all chemical bonds present in a molecule is the energy required forbreaking all the bonds,therefore,option (b), (c) and (d) are incorrect.