Answer
$83.0\,J\,mol^{-1}K^{-1}$
Work Step by Step
We find:
$\Delta S^{\circ}_{vap}=\frac{\Delta H^{\circ}_{vap}}{T_{bp}}=\frac{20.2\,kJ/mol}{(-29.79+273.15)K}$
$=0.0830\,kJ\,mol^{-1}K^{-1}=83.0\,J\,mol^{-1}K^{-1}$
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