Explore BrainMass

Raoult's Law

Raoult’s Law states that the vapor pressure of an ideal solution is dependent on the vapor pressure and mole fraction of each chemical component in the solution. This statement is commonly written as:

p = pA*xA + pB*xB + pC*xC+ ...

p is the total vapor pressure of the ideal solution
A, B and C are different chemical components in the solution
p(where i = A, B, C…) is the vapor pressure of that individual chemical component within the solution.
xi (where i = A, B, C…) is the mole fraction of that individual chemical component within the solution, where the sum of all mole fractions must equal 1.

For example, if a solution is comprised of H2O and glycerin in equal molar amounts then:
p = pglycerin*0.5 + pH2O*0.5

The vapor pressure of glycerin is 0, so the equation can be simplified to:

p = pH2O*0.5

Since, the vapor pressure of HH2O is 54.74 mmHg, then

P = 54.74*0.5 = 27.37 mmHg

Thus, understanding Raoult’s Law is important for understanding chemical reactions in solution, as well as the calculation of the following: total vapor pressure, individual vapor pressure, and individual mole fraction.