Question

For a phase change
$H_{2}O\left(l\right)\stackrel{0{}^{\circ }C,1bar}{\rightleftharpoons }{H}_{2}O\left(s\right)$

• A. $\Delta G=0$
• B. $\Delta S=0$
• C. $\Delta H=0$
• D. $\Delta U=0$

Answer 1

The correct option is A $\Delta G=0$

As, phase change process is at constant pressure, the change in enthalpy is equal to the heat transferred from the surroundings to the system: $\Delta H=q$
And, the phase change process is also at constant temperature, the change in entropy, which is given by the integral of $dq/T$, is:
$\Delta S=\frac{q}{T}=\frac{\Delta H}{T}$
As, $\Delta G=\Delta H-T\Delta S$
$\Rightarrow \Delta G=\Delta H-T\frac{\Delta H}{T}=0$
Thus, for phase change process, $\Delta G=0$