Vapor Pressure Calculator – Calculate Vapor Pressure at Any Temperature

Determine the vapor pressure of a substance at any temperature using our vapor pressure calculator. Based on the Clausius-Clapeyron and Antoine equations, it's ideal for physical chemistry, thermodynamics, and engineering applications.

Method

Temperature (°C)

Enthalpy of Vaporization (kJ/mol)

Reference Temperature (°C)

Reference Pressure (any unit)

Understanding Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase. It increases exponentially with temperature. Higher vapor pressure means a substance evaporates more easily.

Clausius-Clapeyron Equation

ln(P/P₀) = -(ΔH_vap/R) × (1/T - 1/T₀)

Where:

P = Vapor pressure at temperature T
P₀ = Reference vapor pressure at T₀
ΔH_vap = Enthalpy of vaporization (J/mol)
R = Gas constant (8.314 J/(mol·K))
T = Temperature (K)

Antoine Equation

log₁₀(P) = A - (B / (T + C))

Where A, B, C are substance-specific constants and T is in °C.

Water Antoine Constants (P in mmHg)

Substance	A	B	C	Temp Range
Water	8.07131	1730.63	233.426	1-100°C
Ethanol	8.20417	1642.89	230.300	-57-80°C
Benzene	6.90565	1211.033	220.790	8-103°C

Vapor Pressure vs Temperature

Exponential relationship showing how vapor pressure increases with temperature

Enter values and calculate to see the graph

Applications of Vapor Pressure

Predicting boiling points at different pressures
Design of distillation and evaporation processes
Understanding volatility of solvents
Food processing and freeze drying
Pharmaceutical formulation stability
Environmental fate of chemicals

How to Calculate Vapor Pressure

Choose Calculation Method

Select Clausius-Clapeyron for theoretical calculations or Antoine equation for empirical accuracy.

Enter Substance Parameters

Input enthalpy of vaporization and reference data, or Antoine constants for your substance.

Get Vapor Pressure Results

View calculated vapor pressure at your temperature with a complete pressure-temperature graph.

Why Use This Vapor Pressure Calculator

Dual Calculation Methods

Choose between Clausius-Clapeyron for theoretical work or Antoine equation for industry-standard accuracy.

Interactive P-T Graph

Visualize the exponential relationship between vapor pressure and temperature with dynamic plotting.

Common Substance Constants

Built-in Antoine constants for water, ethanol, benzene, and other common solvents.

Boiling Point Prediction

Determine boiling points at various pressures for vacuum distillation and altitude cooking.

Vapor Pressure Equations Reference

Equation	Formula	Best For
Clausius-Clapeyron	ln(P/P₀) = -(ΔH/R)(1/T - 1/T₀)	Theoretical, educational
Antoine	log₁₀(P) = A - B/(T+C)	Industrial, accurate
August-Roche-Magnus	P = 0.61094 × exp(17.625T/(T+243.04))	Water vapor, meteorology

Frequently Asked Questions

What is vapor pressure?

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase. It indicates how readily a substance evaporates—higher vapor pressure means faster evaporation and greater volatility.

How does temperature affect vapor pressure?

Vapor pressure increases exponentially with temperature. As molecules gain kinetic energy, more escape the liquid surface. This is why water boils at lower temperatures at high altitudes where atmospheric pressure is lower.

What is the Antoine equation used for?

The Antoine equation is an empirical formula that accurately predicts vapor pressure over a specific temperature range. It's widely used in chemical engineering for distillation design and process calculations.

How do I find the boiling point from vapor pressure?

A liquid boils when its vapor pressure equals atmospheric pressure. At sea level (760 mmHg), water boils at 100°C. At higher elevations with lower atmospheric pressure, boiling occurs at lower temperatures.

What are Antoine constants for water?

For water (P in mmHg, T in °C): A=8.07131, B=1730.63, C=233.426, valid from 1-100°C. These constants give accurate vapor pressure predictions for water in the liquid range.

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