Question

Which type of deviation (positive or negative) from ideal behaviour will be shown by the solution of cyclohexane and ethanol? Give suitable reasons.

Answer 1

1. A solution of cyclohexane and ethanol shows a positive deviation from ideal behaviour because ethanol molecules, which are polar, normally form strong hydrogen bonds with each other.
2. When cyclohexane, a non-polar molecule, is added, it disrupts these hydrogen bonds without forming equally strong interactions in return.
3. As a result, the intermolecular forces between ethanol and cyclohexane (A-B) are weaker than those in the pure components (A-A and B-B), making it easier for molecules to escape into the vapour phase.
4. This increases the vapour pressure of the solution beyond what is predicted by Raoult’s law, hence showing a positive deviation.