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Clausius-Clapeyron Vapor Pressure & Temperature Calculator

Derived by Rudolf Clausius and Émile Clapeyron, this fundamental thermodynamic relation characterizes discontinuous phase transitions between liquid and gas.

Reference saturation temperature in °C (Water normal boiling point = 100°C).

Reference vapor pressure in kPa (1 atm = 101.325 kPa).

Molar heat of vaporization (Water ≈ 40.66 kJ/mol, Ethanol ≈ 38.56 kJ/mol).

Select whether to solve for target vapor pressure or saturation temperature.

Used when calculating P₂ (e.g., autoclave temperature 120°C).

Used when calculating T₂ (e.g., pressure cooker chamber pressure).

Calculated Result
197.358 kPa

Vapor Pressure (P₂)

Initial State

101.325 kPa @ 100°C (373.1 K)

Enthalpy of Vaporization (ΔHvap)

40.66 kJ/mol

Target Vapor Pressure (P₂)

197.358 kPa

Target Temperature (T₂)

120°C (393.15 K)

Pressure Ratio (P₂/P₁)

1.9478x

Calculation Breakdown

  1. 1. State & Constants ConversionT₁ = 100°C = 373.15 K, P₁ = 101.325 kPa, ΔHvap = 40.66 kJ/mol = 40660 J/mol, R = 8.314 J/(mol·K)
  2. 2. Clausius-Clapeyron Formulationln(P₂ / P₁) = -(ΔHvap / R) · (1/T₂ - 1/T₁)
  3. 3. Solve for P₂P₂ = 101.325 · exp[ -(40660 / 8.314) · (1/393.15 - 1/373.15) ] = 197.358 kPa

Water Vapor Pressure vs Temperature

Interactive visualization based on your current inputs

P (kPa)
0.0509914919980°C90°C100°C (1 atm)110°C120°CTemperature (°C)Vapor Pressure (kPa)

What Is the Clausius-Clapeyron Vapor Pressure & Temperature Calculator?

The Clausius-Clapeyron equation relates the vapor pressure of a pure substance to its temperature during a liquid-gas or solid-gas phase transition.

How Does the Clausius-Clapeyron Vapor Pressure & Temperature Calculator Work?

Derived from chemical potential equality (dμ_liq = dμ_vap), it integrates the Clapeyron differential equation assuming ideal vapor behavior.

Clausius-Clapeyron Vapor Pressure & Temperature Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

\ln\left(\frac{P_2}{P_1}\right) = -\frac{\Delta H_{vap}}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right)

Natural log of pressure ratio equals negative enthalpy of vaporization over universal gas constant R times difference of inverse absolute temperatures.

How to Use the Clausius-Clapeyron Vapor Pressure & Temperature Calculator

  1. Enter the reference temperature (°C) and vapor pressure (kPa).
  2. Provide molar enthalpy of vaporization in kJ/mol.
  3. Select calculation target and supply the target temperature or pressure.

Step-by-Step Example Calculation

Water at 120°C (Autoclave Pressure)

Input Values:

t1Celsius:100
p1KPa:101.325
deltaHVapKJPerMol:40.66
targetMode:calculateP2
t2Celsius:120
Worked Steps: Raising water temperature from 100°C to 120°C increases saturation vapor pressure from 101.3 kPa to 198.5 kPa (~1.96 atm).

Understanding Your Result

Target Vapor Pressure (kPa): Boiling pressure required to maintain equilibrium.

Saturation Temperature (°C): Boiling temperature at the given pressure.

Pressure Ratio: Factor change in vapor pressure between states.

Factors That Affect the Result

  • Enthalpy of vaporization determines the steepness of the exponential pressure-temperature curve.

When Should You Use This Calculator?

  • Chemical distillation, pressure cooker design, meteorology, vacuum drying, and refrigeration engineering.

Assumptions & Limitations

  • Assumes constant ΔHvap over temperature delta, negligible liquid molar volume compared to gas, and ideal gas behavior.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Standard integrated Clausius-Clapeyron model using R = 8.314 J/(mol·K).

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