Fugacity: It is derived from Latin, expressed as fleetness or escaping ...

Non ideal solution
An ideal solution obeys Raoults law and p-x line will be straight. Non ideal solution do
not obey Raoults law. The total pressure for non ideal solutions may be greater or lower
than that for ideal solution. When total pressure is greater than pressure given by Raoults
law, the system shows positive deviation from Raoults law.
Eg: Ethanol-toluene
When the total pressure at equilibrium is less than the pressure given by Roults law the
system shows negative deviation from Raoults law.
Eg: Tetrahydrofuron-ccl4
Azeotropes
Azeotropes are constant boiling mixtures. When the deviation from Raoults law is very
large p-x and p-y curve meets at this point y1=x1 and y2=x2
A mixture of this composition is known as Azeotrope. Azeotrope is a vapour liquid
equilibrium mixture having the same composition in both the phases.
Types of Azeotropes
Azeotropes are classified into two types
1. Maximum curve pressure, minimum boiling azeotropes
2. Minimum pressure maximum boiling azeotrope
The azeotrope formed when negative deviation is very large will exhibit minimum
pressure or maximum boiling point, this is known as minimum pressure Azeotrope.
Eg : Ethanol –water, benzene-ethanol
The azeotrope formed when –ue deviation is very large will exhibit minimum pressure or
maximum boiling point, this is known as minimum pressure azeotrope.
Phase diagram for both types of Azeotropes
Minimum Temperature azeotropes