Q36 / 170 · Manipal (MET) 2018 · Chemistry

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

  • Correct answer
    A
    $109.4 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$
  • B
    $10.94 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$
  • C
    $1.094 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$
  • D
    $1009.4 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$

Solution

$\begin{aligned} & \text { } \Delta S_{\text {vap }}=\frac{\Delta H_{\text {vap }}}{T} \\ & \because \Delta H_{\text {vap }}=40.8 \mathrm{~kJ} \mathrm{~mol}^{-1}, T=373 \mathrm{~K} \\ & \Delta S_{\text {vap }}=\frac{40.8 \times 10^3}{373}=109.4 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\end{aligned}$

Hence, the correct answer is option: 'A'.

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