Chapter 15, Problem 80A

Interpretation Introduction

Interpretation:

Molar enthalpy of fusion of methanol is to be explained..

Concept introduction:

Molar enthalpy of fusion: The heat required to melt one mole of a solid substance is called its molar enthalpy (heat) of fusion ${\text{(ΔH}}_{\text{fus}}^{})$.

Answer to Problem 80A

It means that 3.22 kJ of energy extracted from 1 mole of liquid methanol to cause it to freeze and become 1 mole of solid methanol.

Explanation of Solution

Since ${\text{ΔH}}_{\text{vap}}^{}\text{=}{\text{-ΔH}}_{\text{cond}}^{}$

${\text{ΔH}}_{\text{fus}}^{}\text{=}{\text{-ΔH}}_{\text{solid}}^{}$

Therefore, in order to freeze 1 mole of methanol extract 3.22kJ of energy. And conversely, add 3.22kJ of energy to one mole of solid methanol to cause it to melt and become one mole of liquid methanol.

Conclusion

${\text{ΔH}}_{\text{vap}}^{}\text{=}{\text{-ΔH}}_{\text{cond}}^{}$

${\text{ΔH}}_{\text{fus}}^{}\text{=}{\text{-ΔH}}_{\text{solid}}^{}$