Question

Formation of an ideal solution leads to

• A. increase in entropy
• B. decrease in volume
• C. increase in enthalpy
• D. decrease in entropy

Hint:

For an ideal solution, remember the "two zeros and a positive": \(\Delta H_{mix} = 0\), \(\Delta V_{mix} = 0\), and \(\Delta S_{mix}>0\). The Gibbs free energy of mixing, \(\Delta G_{mix} = \Delta H_{mix} - T\Delta S_{mix}\), will therefore always be negative, indicating a spontaneous process.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
An ideal solution is a theoretical solution where the interactions between molecules of different components are exactly the same as the interactions between molecules of the same components (e.g., A-B interactions are the same as A-A and B-B interactions). The question asks about the thermodynamic changes that occur upon mixing components to form such a solution.
Step 2: Key Properties of Ideal Solution Formation:
The key thermodynamic properties for the formation (mixing) of an ideal solution are:
Enthalpy of mixing (\(\Delta H_{mix}\)): Since the intermolecular forces do not change upon mixing, no heat is absorbed or evolved. Thus, \(\Delta H_{mix} = 0\).
Volume of mixing (\(\Delta V_{mix}\)): The total volume of the solution is simply the sum of the volumes of the individual components. There is no expansion or contraction. Thus, \(\Delta V_{mix} = 0\).
Entropy of mixing (\(\Delta S_{mix}\)): The process of mixing leads to a more disordered or random arrangement of molecules compared to the pure, separated components. An increase in randomness corresponds to an increase in entropy. Thus, \(\Delta S_{mix}>0\).
Step 3: Detailed Explanation:
Let's evaluate the given options based on these properties:
- (A) increase in entropy: This is correct. The mixing of different types of molecules always increases the system's disorder, hence entropy increases (\(\Delta S_{mix}>0\)).
- (B) decrease in volume: This is incorrect. For an ideal solution, the volume of mixing is zero (\(\Delta V_{mix} = 0\)).
- (C) increase in enthalpy: This is incorrect. For an ideal solution, the enthalpy of mixing is zero (\(\Delta H_{mix} = 0\)).
- (D) decrease in entropy: This is incorrect. Mixing is a spontaneous process that increases disorder.
Step 4: Final Answer:
The formation of an ideal solution leads to an increase in entropy.
Step 5: Why This is Correct:
The fundamental characteristic of any mixing process, ideal or non-ideal, is the increase in randomness of the system, which corresponds to a positive change in entropy. The other options describe properties that are specifically zero for an ideal solution or are thermodynamically incorrect.