Vapor Pressure Calculator

Vapor Pressure Formula:

\[ P = P° \times \exp\left(-\frac{\Delta H_{vap}}{R} \times \left(\frac{1}{T} - \frac{1}{T_b}\right)\right) \]

Reference Pressure (P°):

Enthalpy of Vaporization (ΔH_vap):

J/mol

Temperature (T):

Boiling Point (T_b):

Vapor Pressure (P): Pa

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is a Vapor Pressure Calculator?

Definition: This calculator estimates the vapor pressure of a liquid using the Clausius-Clapeyron equation.

Purpose: It helps chemists, engineers, and researchers determine the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature.

2. How Does the Calculator Work?

The calculator uses the Clausius-Clapeyron equation:

\[ P = P° \times \exp\left(-\frac{\Delta H_{vap}}{R} \times \left(\frac{1}{T} - \frac{1}{T_b}\right)\right) \]

Where:

\( P \) — Vapor pressure (Pa)
\( P° \) — Reference pressure (typically 1 atm = 101325 Pa)
\( \Delta H_{vap} \) — Enthalpy of vaporization (J/mol)
\( R \) — Gas constant (8.314 J/mol·K)
\( T \) — Temperature (K)
\( T_b \) — Boiling point at reference pressure (K)

Explanation: The equation relates the vapor pressure to temperature, accounting for the energy required to vaporize the liquid.

3. Importance of Vapor Pressure Calculation

Details: Vapor pressure is crucial for understanding evaporation rates, boiling points, and the behavior of substances in different environmental conditions.

4. Using the Calculator

Tips: Enter the reference pressure (default 101325 Pa), enthalpy of vaporization (default 40660 J/mol for water), temperature in Kelvin, and boiling point at reference pressure (default 373 K for water).

5. Frequently Asked Questions (FAQ)

Q1: What is the Clausius-Clapeyron equation?
A: It's a thermodynamic relationship that describes how vapor pressure changes with temperature for a liquid-vapor phase transition.

Q2: What's a typical enthalpy of vaporization?
A: For water it's 40.66 kJ/mol (40660 J/mol), but values vary by substance (e.g., ethanol: 38.56 kJ/mol).

Q3: Why use Kelvin for temperature?
A: The equation requires absolute temperature to properly account for thermodynamic relationships.

Q4: How accurate is this calculation?
A: It provides good estimates for many liquids, but assumes ΔH_vap is constant over the temperature range.

Q5: Can I use this for solids?
A: The equation can be adapted for sublimation, but you would need the enthalpy of sublimation instead.