Question

$\Delta H_{vap}=30\text{kJ/mol}$ and $\Delta S_{vap}=75{\text{J mol}}^{-1}{\text{K}}^{-1}$. Find the temperature of vapour, at one atmosphere:

• A. $400\text{K}$
• B. $350\text{K}$
• C. $298\text{K}$
• D. $250\text{K}$

Answer 1

The correct option is A $400\text{K}$

By using the relation,
$\Delta H_{vap}=T\Delta S_{vap}$
$T=\frac{\Delta H_{vap}}{\Delta S_{vap}}$
Given,
$\Delta H_{vap}=30\text{kJ/mol}=30,000\text{J/mol}$
$\Delta S_{vap}=75{\text{J mol}}^{-1}{\text{K}}^{-1}$
$T=\frac{30,000}{75}$
$T=400\text{K}$