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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+ ...

where,
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.

Activities and activity coefficients

By measuring the equilibrium between liquid and vapor phases of a solution at 30°C at 1.00 atm, it was found that xA = 0.220 when yA = 0.314. Calculate the activities and activity coefficients of both components in this solution on the Raoult's law basis. The vapor pressures of the pure components at this temperature are P*A =

Vapor Pressures

Consider two solutions, one formed by adding 10 g of glucose ( C6H12O6) to 1L of water an another formed by adding 10 g of sucrose (C12H22O11) to 1 L of water. Are the vapor pressures over the two solutions the same? Why or why not?