Question

Which condition is not satisfied by an ideal solution?
A.${\Delta _{mix}}H{\text{ }} = {\text{ }}0$
B. ${\Delta _{mix}}{\text{V }} = {\text{ }}0$
C. ${\Delta _{mix}}S{\text{ }} = {\text{ }}0$
D. Obeyance to Raoult’s Law

Answer 1

The solutions which obey Raoult’s Law at every range of concentration and at all temperatures are called ideal solutions. The solution is said to be an ideal solution, only when the intermolecular forces of attraction between A – A, B – B and A – B are nearly equal.
Complete step by step answer: Consider two liquids A and B, and mix them. The formed solution will experience several intermolecular forces of attractions inside it, which will be:
A – A intermolecular forces of attraction
B – B intermolecular forces of attraction
A – B intermolecular forces of attraction
They follow Raoult’s Law, which means partial pressure of components A and B in a solution will be ${P_A}\; = {\text{ }}{P_A}^0\;{x_A}\;$ and ${P_B}\; = {\text{ }}{P_B}^0\;{x_{B{\text{ }}\;}}$ where $\;{P_A}^0\;$ and $\;{P_B}^0\;$ are respective vapour pressure in pure form and xA and xB are respective mole fractions of components A and B
The enthalpy of mixing of two components should be zero, that is, ${\Delta _{mix}}H{\text{ }} = {\text{ }}0$.
This signifies that no heat is released or absorbed during mixing of two pure components to form ideal solution
The volume of mixing of two components should be zero, that is, ${\Delta _{mix}}V{\text{ }} = {\text{ }}0$.
This means that the total volume of solution is equal to the sum of the volume of solute and solution. Adding further, it also signifies that there is no occurrence of contraction or expansion of volume while mixing of two components
Hence, ${\Delta _{mix}}S{\text{ }} = {\text{ }}0$ condition is not satisfied with an ideal solution.

Hence the correct option is (C)

Note: The conditions followed by an ideal solution are as follows:
Volume change ($\Delta V$) for the mixture of two components should be zero.
Ideal solutions always obey Raoult's law at every range of concentration.