A liquid mixture of A and B shows positive deviation from Raoult’s law when 

When A – B interactions are weaker than A – A and B – B interactions, then the mixture of A and B shows positive deviation ;

Vapour pressure of the mixture is more than expected from Raoult's law;

$∆{\mathrm{V}}_{\mathrm{mix}}>0, ∆{\mathrm{H}}_{\mathrm{mix}}>0, ∆{\mathrm{S}}_{\mathrm{mix}}>0, ∆{\mathrm{G}}_{\mathrm{mix}}<0 ;$