Calculate how vapor pressure changes with temperature or determine the enthalpy of vaporization.
System Parameters
K
K
kJ/mol
Calculation Results
Enter the required parameters to calculate the final vapor pressure
About this calculator
Overview
The Clausius-Clapeyron equation is the mathematical reason why pressure cookers cook food faster and why water boils at a lower temperature on Mount Everest. It describes the steep, exponential relationship between temperature and the vapor pressure of a substance.
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Pro Tips
Always convert temperatures to Kelvin (K = °C + 273.15). The equation will fail with Celsius.
Pressure units (atm, torr, Pa) don't matter as long as Pâ and Pâ matchâthe ratio Pâ/Pâ is unitless.
Enthalpy of Vaporization (ÎHvap) must be in J/mol for the calculation (we auto-convert from kJ/mol for you).
This equation assumes ÎHvap is constant over the temperature range, which is a good approximation for small ranges.
Water's ÎHvap is ~40.65 kJ/mol at 100°C.
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Fun Facts
"Pressure cookers work by trapping steam to raise the pressure. This forces the boiling point of water up to ~120°C, cooking food much faster."
"On Mars, the polar ice caps are made of dry ice (frozen COâ). They don't meltâthey 'sublimate' directly from solid to gas, creating huge winds and 'Swiss cheese' terrain."
"Rubbing alcohol feels cold on your skin because it evaporates quickly (high vapor pressure). As it leaves, it takes heat energy with it!"
"If you tried to cook pasta on Mount Everest, the water would boil at just 70°C. Your pasta would turn into a mushy, undercooked mess."
"Charles Darwin once complained that his potatoes wouldn't cook properly high in the Andes mountainsâhe was experiencing Clausius-Clapeyron firsthand!"
"The equation predicts that for every 1°C of warming, the atmosphere can hold ~7% more water vapor, fueling more intense storms."
"It applies to solids too! The smell of mothballs is caused by sublimation, which this equation also models."
