Question

The enthalpy of vaporisation of liquid diethyl ether ${\left(C_2{H}_5\right)}_{2}O$ is $26kJ{mol}^{-1}$ at its boiling point ${35}^{o}C$. Calculate $\Delta S^o$ for conversion of:
(a) liquid to vapour
(b) vapour to liquid at ${35}^{o}C$

Answer 1

(a) $\Delta S_{vapourisation}=\frac{\Delta H_{vapourisation}}{T_{bp}}=\frac{26000}{308}=84.42J{K}^{-1}{mol}^{-1}$
(b) $\Delta S_{condensation}=-\Delta S_{vapourisation}=-84.42J{K}^{-1}{mol}^{-1}$