Question

In case of positive deviation from Raoult's law, the intermolecular attractive forces between the solute-solvent molecules as compared to those between the solute-solute and solvent-solvent molecules are

• A. weaker
• B. stronger
• C. same
• D. independent of intermolecular forces between solute-solvent molecules.

Hint:

Positive deviation $\longrightarrow$ weaker attraction $\longrightarrow$ higher vapor pressure $\longrightarrow$ lower boiling point.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Raoult's Law describes the vapor pressure of ideal solutions. Deviations occur when the interactions between different molecules (\(A-B\)) differ from interactions between like molecules (\(A-A\) or \(B-B\)).
Step 2: Detailed Explanation:
In a solution showing positive deviation:
The observed vapor pressure is higher than predicted by Raoult's law. This happens because the molecules can escape into the vapor phase more easily than in their pure states.
This increased escaping tendency is a result of the solute-solvent (\(A-B\)) attractive forces being weaker than the solute-solute (\(A-A\)) and solvent-solvent (\(B-B\)) attractive forces.
Because the different molecules don't "hold onto" each other as strongly, they transition to the gas phase more readily, increasing vapor pressure.
Step 3: Final Answer:
Solute-solvent attractive forces are weaker.