Vapour Pressure Calculator:
Enter the values of Mole Fraction of the Solvent, MFsolvent and Vapour Pressure of the pure Solvent, VPsolvent to determine the value of Vapour Pressure of a Solution, VPsolution.
Vapour Pressure Formula:
Vapour pressure is the pressure exerted by the vapour of a substance in equilibrium with its liquid or solid form at a given temperature. It is a measure of a liquid’s tendency to evaporate and form a vapour. The higher the vapour pressure of a liquid at a given temperature, the more volatile it is and the easier it is for the liquid to evaporate.
In a solution, the vapour pressure depends on the components of the mixture. When a non-volatile solute is dissolved in a solvent, the vapour pressure of the solution decreases compared to the pure solvent. This phenomenon is explained by Raoult’s Law, which states that the vapour pressure of a solution is directly proportional to the mole fraction of the solvent in the solution.
The decrease in vapour pressure is due to the reduction in the number of solvent molecules available at the surface to evaporate, as some surface molecules are replaced by solute particles. This principle is crucial in various applications, such as boiling point elevation, freezing point depression, and distillation processes.
Vapour Pressure of a Solution, VPsolutionin millimetres of mercury is the product of the Mole Fraction of the Solvent, MFsolvent in the solution and the Vapour Pressure of the pure Solvent, VPsolvent in millimetres of mercury.
Vapour Pressure of a Solution, VPsolution = MFsolvent * VPsolvent
VPsolution = vapour pressure of a solution in millimetres of mercury, mmHg.
MFsolvent = mole fraction of a solvent.
VPsolvent = vapour pressure of a solvent in millimetres of mercury, mmHg.
Vapour Pressure Calculation:
1.A solution mole fraction of a solvent 0.9. The vapour pressure of the pure solvent is 250 mmHg. Calculate the vapour pressure of the solution.
Given: MFsolvent = 0.9, VPsolvent = 250mmHg.
Vapour Pressure of a Solution, VPsolution = MFsolvent * VPsolvent
VPsolution = 0.9 * 250
VPsolution = 225mmHg.
2.The vapour pressure of a solution is 180 mmHg, and the mole fraction of the solvent is 0.8. Calculate the vapour pressure of the pure solvent.
Given: MFsolvent = 0.8, VPsolution = 180mmHg.
Vapour Pressure of a Solution, VPsolution = MFsolvent * VPsolvent
VPsolvent = VPsolution / MFsolvent
VPsolvent = 180 / 0.8
VPsolvent = 225mmHg.