Question

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

• A. $109.4 \,JK ^{-1} \,mol ^{-1}$
• B. $10.94 \,JK ^{-1}\, mol ^{-1}$
• C. $1.094 \,JK ^{-1} \,mol ^{-1}$
• D. $1009.4 \,JK ^{-1} \,mol ^{-1}$

Answer 1

Answer: (A)

$\Delta S _{\text {vap }}=\frac{\Delta H _{\text {vap }}}{ T }$
$\because \Delta H _{\text {vap }}=40.8\, kJ\, mol ^{-1}, T =373 \,K$
$\Delta S _{\text {vap }}=\frac{40.8 \times 10^{3}}{373}=109.4 \,JK ^{-1}\, mol ^{-1}$