Vapor Pressure Curve Simulation

Interactive demonstration of Clausius-Clapeyron equation and liquid-vapor equilibrium

Graph Type

Substances

Liquid-Vapor Equilibrium

Evaporation Rate: 0 Condensation Rate: 0
Temperature: 25 °C
Vapor Pressure: 0 atm
Boiling Point: -- °C
ΔHvap: -- kJ/mol
Drag to see how vapor pressure changes with temperature

Parameters

Physical Equations

Clausius-Clapeyron: ln(P) = -ΔHvap/(R·T) + C
Exponential Form: P = P₀ · e^(-ΔHvap/R·T)
Two-Point Form: ln(P₂/P₁) = -ΔHvap/R · (1/T₂ - 1/T₁)
Gas Constant: R = 8.314 J/(mol·K)

Substance Properties

Substance Boiling Point ΔHvap (Enthalpy of Vaporization) Vapor Pressure at 25°C (atm)

What is Vapor Pressure?

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 molecules in a liquid have enough kinetic energy to overcome intermolecular forces and escape into the gas phase, they create vapor pressure.

Clausius-Clapeyron Equation

The Clausius-Clapeyron equation describes the relationship between vapor pressure and temperature: ln(P) = -ΔHvap/(R·T) + C, where ΔHvap is the enthalpy of vaporization, R is the gas constant, T is the absolute temperature, and C is an integration constant. In semi-log coordinates (ln P vs 1/T), this equation produces a straight line with slope = -ΔHvap/R.

Boiling Point

The boiling point is the temperature at which the vapor pressure equals the external pressure (typically 1 atm). At this temperature, bubbles can form throughout the liquid, not just at the surface. Substances with weaker intermolecular forces have lower boiling points and higher vapor pressures at a given temperature.

Factors Affecting Vapor Pressure

Vapor pressure depends on: (1) Temperature - higher temperatures increase molecular kinetic energy and vapor pressure exponentially; (2) Intermolecular forces - stronger forces (hydrogen bonding, dipole-dipole) result in lower vapor pressures; (3) Molecular size - larger molecules typically have stronger London dispersion forces and lower vapor pressures. This explains why diethyl ether boils at 34.6°C while water boils at 100°C despite both being polar molecules.

Applications

Understanding vapor pressure is crucial in: Distillation processes for separating liquids based on different boiling points, pressure cooking (increased pressure raises boiling point), vacuum distillation for heat-sensitive compounds, meteorology (humidity and dew point), preservation of food and pharmaceuticals, and design of refrigeration and air conditioning systems. The Clausius-Clapeyron equation is fundamental to phase equilibrium calculations in chemical engineering and thermodynamics.