Question

Explain with a suitable diagram and appropriate examples why some non-ideal solutions show positive deviation from ideal behaviour.

Answer 1

Let us consider the problem.

Vapour pressures of two component system as a function of composition.

The solution shown positive deviation ideal behaviour when the interaction between the unlike molecules is weaker than the like molecules therefore interaction between A to B molecules is weak than A to A and B to B molecules.

In this case, the molecules find it more easy to escape an thus the vapour pressure of the solution is higher than expected.

For example:Acetone mixed with ethanol, energy is required to break hydrogen bonds between ethanol molecules.