Question

The enthalpy change, for the transition of liquid water to steam, $\Delta H_{vapour}$ is $40.8kJ{mol}^{-1}$ at $373K$. Calculate the entropy change for the process.

Answer 1

The transition under consideration is:
$H_{2}O\left(l\right)⟶H_{2}O\left(g\right)$
We know that, $\Delta S_{vapour}=\frac{\Delta H_{vapour}}{T}$
given, $\Delta H_{vapour}=40.8kJ{mol}^{-1}$
$=40.8\times 1000J{mol}^{-1}$
$T=373K$
Thus $\Delta S_{vapour}=\frac{40.8\times 1000}{373}=109.38J{K}^{-1}{mol}^{-1}$