Question -
Answer -
According to Raoult’s law, thepartial vapour pressure of each volatile component in any solution is directlyproportional to its mole fraction. The solutions which obey Raoult’s law overthe entire range of concentration are known as ideal solutions. Thesolutions that do not obey Raoult’s law (non-ideal solutions) have vapourpressures either higher or lower than that predicted by Raoult’s law. If thevapour pressure is higher, then the solution is said to exhibit positivedeviation, and if it is lower, then the solution is said to exhibit negative deviationfrom Raoult’s law.
Vapour pressure of a two-component solution showingpositive deviation from Raoult’s law
Vapour pressure of a two-component solution showingnegative deviation from Raoult’s law
In the case of an ideal solution,the enthalpy of the mixing of the pure components for forming the solution iszero.
ΔsolH = 0
In the case of solutions showingpositive deviations, absorption of heat takes place.
∴ΔsolH = Positive
In the case of solutions showingnegative deviations, evolution of heat takes place.
∴ΔsolH = Negative