Enter your Initial Temperature (T₁), Initial Pressure (P₁), Final Temperature (T₂), ΔH, and Gas Constant (R) into the Clausius-Clapeyron Calculator to find Final Pressure (P₂) — plus the Pressure Ratio, Temperature Change (ΔT), and ln(P₂/P₁) showing how vapor pressure shifts with temperature.
Final Pressure (P₂)
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Pressure Ratio (P₂/P₁)
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Temperature Change (ΔT)
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ln(P₂/P₁)
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The Clausius-Clapeyron equation describes the relationship between vapor pressure and temperature during phase transitions. It's expressed as ln(P₂/P₁) = -ΔH/R × (1/T₂ - 1/T₁), where P is pressure, T is temperature, ΔH is enthalpy of vaporization, and R is the gas constant.
Vapor pressure is the pressure exerted by vapor molecules in equilibrium with their liquid phase at a given temperature. It increases with temperature and varies by substance based on intermolecular forces and molecular weight.
Enthalpy of vaporization (ΔH) is the energy required to convert one mole of liquid into vapor at constant temperature and pressure. It's a measure of how strongly molecules are held together in the liquid phase.
The boiling point occurs when vapor pressure equals atmospheric pressure. Using the Clausius-Clapeyron equation, you can calculate the temperature at which vapor pressure reaches 101,325 Pa (1 atm) by rearranging the equation to solve for T₂.
Higher vapor pressure leads to lower boiling points. At higher altitudes where atmospheric pressure is lower, liquids boil at lower temperatures because their vapor pressure reaches atmospheric pressure sooner.
At 60% atmospheric pressure (approximately 60,795 Pa), water would boil at about 85°C (358K). This demonstrates how reduced pressure lowers the boiling point, which is why cooking takes longer at high altitudes.
The universal gas constant R (8.314 J/mol·K) appears in the denominator of the Clausius-Clapeyron equation. It relates the energy scale (enthalpy of vaporization) to the temperature and pressure changes during phase transitions.