Calculate vapor pressure of ideal solutions using Raoult's law. Determine partial pressures, total pressure, and vapor composition for binary solutions.
Total Vapor Pressure
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Partial Pressure A
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Partial Pressure B
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Vapor Mole Fraction A
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Vapor Mole Fraction B
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Raoult's law is used to calculate the vapor pressure of ideal solutions and predict how adding a solute affects the vapor pressure of a solvent. It's essential in distillation, chemical engineering, and understanding solution behavior.
Raoult's law states that the partial vapor pressure of a component in an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution.
The equation is P_i = x_i × P°_i, where P_i is the partial pressure of component i, x_i is its mole fraction, and P°_i is the vapor pressure of pure component i.
Rearrange the equation to x_i = P_i / P°_i. You need to know the partial pressure of the component and the vapor pressure of the pure component to calculate the mole fraction.
The vapor pressure depends on the pure component's vapor pressure. Use P_solution = x_solvent × P°_solvent. If the pure solvent has a vapor pressure of 100 mmHg, then P_solution = 0.86 × 100 = 86 mmHg.
Raoult's law only applies to ideal solutions. It fails for solutions with strong intermolecular interactions, electrolytes, or when components have significantly different molecular sizes or polarities.
Partial pressure is the pressure exerted by each individual component in the vapor phase. Total pressure is the sum of all partial pressures according to Dalton's law.
Calculate each partial pressure using Raoult's law, then find the vapor mole fraction: y_i = P_i / P_total. The vapor composition differs from liquid composition due to different volatilities.