Question

For a liquid, enthalpy of fusion is $1.435kcalmo{l}^{-1}$ and molar entropy change is $5.26calmo{l}^{-1}{K}^{-1}$ The melting point of the liquid is:

• A. ${100}^{\circ }C$
• B. $0^{\circ }C$
• C. ${273}^{\circ }C$
• D. ${373}^{\circ }C$

Answer 1

The correct option is B $0^{\circ }C$

We know that,
$△S_{fusion}=\frac{△H_{fusion}}{T_{m.p.}}$
$T_{m.p.}$ is the melting point.
$△H_{fusion}=1435cal/mol$

putting all the values,
$T_{m.p.}=\frac{1435}{5.26}=273K=0^{\circ }C$


Theory:

Entropy Calculation with phase transformation:
Phase change occurs at constant Pressure & Temperature and is considered reversible if it occurs at its transition temperature.

Entropy change for Fusion:
At constant pressure, $q=q_p$ = $\Delta H$
$\Delta S_{fusion}$ = $\frac{\Delta H_{fusion}}{T_{m.p.}}$ where $T$ is melting point of a substance.