Question

The thermodynamic parameters for the mixing of benzene and naphthalene are:

• A. $\Delta G$ is positive
• B. $\Delta S_{\text{system}}$ is positive
• C. $\Delta S_{\text{surrounding}}$ is zero
• D. $\Delta H$ is zero

Answer 1

Answer: (B), (C), (D)

The correct options are
B $\Delta S_{\text{system}}$ is positive
C $\Delta S_{\text{surrounding}}$ is zero
D $\Delta H$ is zero

Benzene and naphthalene form ideal solution.
For an ideal solution, since A-A interactions and B-B interactions are equal hence $\Delta H$, change in enthalpy is zero and no heat is absorbed or released.

Entropy of the system increases due to mixing.

Free energy is given by,
$\Delta G=\Delta H-T\Delta S_{\text{system}}$
Since $\Delta H$ is zero, $\Delta S_{\text{system}}$ is positive, so free energy is negative.


Since $\Delta H$ is zero,
$\therefore \Delta S_{\text{surrounding}}=\frac{\Delta H}{T}=0$