What is meant by positive and negative deviations from Raoult's law and how is the sign of mix ∆sol H related to positive and negative deviations from Raoult's law?

What is meant by positive and negative deviations from Raoult's law and how is the sign of mix ∆_sol H related to positive and negative deviations from Raoult's law?

Solution

Solutions showing positive deviations from Raoult's law: Let Take a  binary solution with have components A and B. If the force of attraction between molecular of and A and B in the solution are weaker than that of between  A — A and B — B, then the tendency of escaping of molecules A—B from the solution becomes more than that of pure liquids. The total pressure of the solution will be greater than the corresponding vapour pressure of ideal solution of the same component  A and B. This type of solution shows positive deviation from Raoult's law. The positive deviation  of solution have been shown in figure. Some energy loose when we mix both solutions. This reaction is endothermic reaction. For Endothermic reaction delta H is always positive

 

Solutions showing negative deviations from Raoult's law : Let Take a  binary solution with have components A and B. If the force of attraction between molecular of and A and B in the solution are stronger  than that of between  A — A and B — B, then the tendency of escaping of molecules A—B from the solution becomes less than that of pure liquids. The total pressure of the solution will be lower than the corresponding vapour pressure of ideal solution of the same component  A and B. This type of solution shows negative deviation from Raoult's law. The negative deviation  of solution have been shown in figure. Some energy released when we mix both solutions. This reaction is exothermic reaction. For Exothermic reaction delta H is always negative