Positive deviation from Raoult ’ s Law
o Volume of the entire solution = Sum of volumes of the components .
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In case of pure components the intermolecular attractive interactions is of A-A and B-B type .
In case of binary solutions the intermolecular attractive interactions is of A-A , B-B and A-B type .
When the intermolecular attractive forces between the A-A and B-B type are nearly equivalent to the intermolecular attractive forces between A-B it results in the formation of ideal
No solution is perfectly ideal but some solutions are nearly ideal in behaviour . For instance , solution of n-hexane and n-heptane , Bromo ethane and chloromethane , benzene and toluene , etc . exhibits ideal behaviour .
The solutions that do not obey Raoult ’ s law over the whole collection of concentration are known as non-ideal solutions .
The vapour pressure of a non-ideal solution is either higher or lower than predicted by Raoult ’ s law .
Positive deviation from Raoult ’ s Law
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The solute- solute and solvent-solvent interaction are stronger than solute-solvent interaction .
Let pA = Partial vapour pressures of component A
PB = Partial vapour pressures of component B
Hmix = Change in enthalpy of mixing .
Vmix = Change in volume of mixing . o o pA > pA o xA
pB > pB o xB