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What is a positive deviation from Raoult’s law and its example?

Answer
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Hint :The French chemist Francois Marte Raoult gives the quantitative relationship between partial pressure and mole fraction of two component solution .according to the Raoult’s law “the partial vapour pressure of each component of volatile liquid is equal to product of the vapour pressure of pure component of solution and its mole fraction”.

Complete Step By Step Answer:
When we take a solution of two components, say A and B. If the force of attraction between AB is weaker than AA and BB in the solution, then the escaping tendency of molecules of components from solution increases and becomes more than the escaping tendency of pure liquid.
As a result, each component of solution has a partial vapour pressure greater than expected.
When the total vapour pressure of solution becomes more than expected, vapour pressure of pure liquid on the basis of Raoult’s law is termed as positive deviation.
pA>pAxA And pB>pBxB
Where PA and PB is vapour pressure of component
PAand PB is Vapour pressure of pure component
xAand xB is Mole fraction of components
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Conditions of solution with positive deviation –
ΔHmixing for these solutions is not zero because energy is required in order to break the bond between AA and BB. Hence, the dissolution process of such a solution is endothermic.
ΔVmixing for these solutions is not zero because the magnitude of intermolecular forces between the components in solution is decreased which means that particles are loosely held in solution . Therefore, there will be an increase in the volume of solution on mixing. Thus, ΔVmixing is positive.
EXAMPLES-
-ethyl alcohol and cyclohexane
-acetone and carbon disulphide
-benzene and acetone
-chloroform and carbon tetrachloride
-acetone and ethyl alcohol
-ethyl alcohol and water

Note :
Non-ideal solutions have a tendency to show positive deviation as well as negative deviation. Solution showing negative deviation includes- acetone –chloroform, chloroform –diethyl ether, chloroform- nitric acid, acetone- aniline etc. in negative deviation ΔHmixing and ΔVmixing shows negative values.