Question

What is the Positive Deviation from Raoult’s Law?

Answer 1

Raoult's Law

1. According to Raoult's Law, in a solution, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction.
2. Mathematically,

$\mathrm{P}\propto \mathrm{x}$

$\mathrm{P}=\mathrm{P}°\mathrm{x}$

where $\mathrm{P}$ = Partial vapour pressure

$\mathrm{P}°$= Vapour pressure of pure component

x = mole fraction of a component

Positive Deviations in Raoult's law

1. Positive Deviation = The condition in which the vapour pressure observed is greater than predicted and occurs when the A-B molecular interaction forces are lower than the attraction of the corresponding average of A-A (the interactions of two same molecules A)and B-B( interaction of two same molecules B) molecules in the mixture.
2. For example, a mixture of ethanol(${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$) and acetone(${\mathrm{CH}}_3{\mathrm{COCH}}_3$)${\mathrm{P}}_{\mathrm{A}}>{\mathrm{P}}_{\mathrm{A}}°{\mathrm{x}}_{\mathrm{A}}\mathrm{and}{\mathrm{P}}_{\mathrm{B}}>{\mathrm{P}}_{\mathrm{B}}°{\mathrm{x}}_{\mathrm{B}}$ $∆{\mathrm{H}}_{\mathrm{mix}}=\mathrm{Positive}$
3. The graph showing a positive deviation for Raoult's law given below-