Question

Why do certain solutions show positive deviation from Raoult’s law?

Answer 1

1. Positive deviations are shown by those liquid pairs for which the A-B molecular interaction forces are weaker than the A-A or B-B interactions in the pure components.
2. As a result of these weaker interactions, the molecules of liquid A or B can escape more easily from the solution than from their respective pure states.
3. This leads to an increase in the vapour pressure of the solution.
4. Therefore, such a solution shows a positive deviation from Raoult’s law, exhibiting a higher vapour pressure than predicted.