Question

For a solution to form positive deviation,the solute-solvent interactions must be less than solute-solute and solvent-solvent interactions,making it easier for the molecules to escape in its pure form.still,why does the vapour pressure of the solution showing positive deviation increase compared to the pure form?

Answer 1

Positive deviations :
In these type of deviations,the partial vapour pressure of each component A and B of solution is higher than the vapour pressure calculated from Raoult's law,
For eg : Water and ethanol,chloroform and water.
In the case of positive deviation A-B interactions are weaker than those between A-A or B-B.This means that in such solutions molecules of A (or B) will find it easier to escape than in pure state.This will increase the vapour pressure and results in the positive deviation from Raoult's law

ΔHmin=+ve