What is meant by positive and negative deviations from Raoult's law and how is the sign of ΔmixH related to positive and negative deviations from Raoult's law?
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Solution
Positive deviation from Raoult's law occurs when the total vapour pressure of the solution is more than corresponding vapour pressure in case of ideal solution.
P=PA+PB>PoAXA+PoBXB
Negative deviation from Raoult's law occurs when the total vapour pressure of the solution is less than corresponding vapour pressure in case of the ideal solution.
P=PA+PB<PoAXA+PoBXB
For positive deviation from Raoult's law, ΔmixH has a positive sign.
For negative deviation from Raoult's law, ΔmixH has a negative sign.