Raoult’s Law Calculator
Raoult's Law Calculator
Calculate the vapor pressure of an ideal solution containing a non-volatile solute.
Pₛₒₗᵤₜᵢₒₙ = Xₛₒₗᵥₑₙₜ * P°ₛₒₗᵥₑₙₜ
Ensure the vapor pressure unit is consistent.
Vapor Pressure in Solutions: A Guide to Raoult's Law
Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. When a non-volatile solute (a substance that does not readily evaporate, like salt or sugar) is dissolved in a volatile solvent (like water), it lowers the solvent's vapor pressure. This phenomenon, known as vapor pressure lowering, is a colligative property, meaning it depends on the concentration of solute particles, not their identity. Raoult's Law provides a simple mathematical relationship to predict the vapor pressure of such an ideal solution.
The law states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture. For a solution with a non-volatile solute, this simplifies to state that the vapor pressure of the solution is directly proportional to the mole fraction of the solvent. This calculator allows you to easily compute the new vapor pressure of a solution, making it a valuable tool for chemistry students studying colligative properties and for scientists working with solutions.
Raoult's Law for a Non-Volatile Solute
The simplified form of Raoult's Law is:
Pₛₒₗᵤₜᵢₒₙ = Xₛₒₗᵥₑₙₜ * P°ₛₒₗᵥₑₙₜ
Where:
- Pₛₒₗᵤₜᵢₒₙ is the vapor pressure of the solution.
- Xₛₒₗᵥₑₙₜ is the mole fraction of the solvent.
- P°ₛₒₗᵥₑₙₜ is the vapor pressure of the pure solvent at the same temperature.
The mole fraction of the solvent (Xₛₒₗᵥₑₙₜ) is calculated as: Moles of Solvent / (Moles of Solute + Moles of Solvent).
Why Does Vapor Pressure Lowering Occur?
Vapor pressure lowering happens because the solute particles at the surface of the solution physically block some of the solvent molecules from escaping into the gas phase. With fewer solvent molecules able to evaporate at any given moment, the pressure exerted by the vapor decreases. The more solute particles present (i.e., the higher the solute concentration), the greater this effect, and the lower the vapor pressure of the solution.