Previous Year NEET Question- Solution L-10

Question: Which one of the following is incorrect for ideal solution?#

A) $\Delta H_{\text {mix }}=0$

B) $\Delta U_{\text {mix }}=0$

C) $\Delta P=P_{\text {obs. }}-P_{\text {calculated by Raoult’s law }}=0$

D) $\Delta G_{\text {mix }}=0$

Answer: $\Delta G_{\text {mix }}=0$#

Solution:#

Key Idea For this problem, the following expression can be used. $$ \Delta G_{\text {mix }}=\Delta H_{\text {mix }}-T \Delta S_{\text {mix }} $$

For an ideal gas $$ \Delta H_{\text {mix }}=0 ; \Delta U_{\text {mix }}=0 ; \Delta S_{\text {mix }} \neq 0 $$

Putting all these values in the expression, $$ \begin{alignedat} & \Delta G_{\text {mix }}=\Delta H_{\text {mix }}-T \Delta S_{\text {mix }} \ & \Rightarrow \quad \Delta G_{\text {mix }}=0+T \Delta S_{\text {mix }} & \therefore \quad \Delta G_{\text {mix }} \neq 0 \end{aligned} $$

Thus, option (d) is incorrect.