Question

Define -Raoult's law.

Answer 1

a law stating that the vapour pressure of an ideal solution is proportional to the mole fraction of solvent.

Answer 2

Hey there!

Answer:


$\textbf{Raoult's Law}$: At a given temperature, for a solution of volatile liquids, the partial vapour pressure of each component in solution is equal to the product of the vapour pressure of the pure component and it's mole fraction.


Let's us consider a binary solution of two volatile liquids and denote the components A and B having the mole fraction $x_{A}$ and $x_{B}$ respectively. If $P_{A}$ and $P_{B}$ are the vapour pressure of the two components in the solution, then according to the above Raoult's Law.


$P_{A} = P_{A}° x_{A}\\ \\ P_{B} = P_{B}° x_{B}\\ \\ Here\: P_{A}° \:and \:P_{B}°\: is \: vapour \:pressure\: of pure\: components \:of \:A \:and \:B. \\ \\ Now, \:According\: to \:Dalton \:partial \:pressure:\\ \\ P = P_{A} + P_{B} \\ \\ Substituting \:the\: values\: of \:P_{A} \:and \:P_{B}\: we \:get:\\ \\ P = P_{A}°x_{A} + P_{B}° x_{B} \\ \\ As \:we \:know :\\ \\ x_{A} + x_{B} = 1\: or \: x_{A} = 1 - x_{B}\\ \\ So:\\ \\ P = P_{A}° ( 1 - x_{B} ) + P_{B}° x_{B}.....( 1 )$


From equation ( 1 ) the following conditions can be drawn:

1) The total vapour pressure of the solution can be related to the mole fraction of any one component.

2) Total vapour pressure of the solution varies linearly with the mole fraction of component B.

3) Depending on the vapour pressure of the pure components A and B, total vapour pressure over the solution decreases or increases with the increase in the mole fraction of component A.



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