Vapor Pressure Calculator

Find a liquid's vapor pressure at another temperature.

How the Math Works

The vapor pressure calculator uses the Clausius-Clapeyron equation to determine how a substance's vapor pressure changes with temperature. The formula P₂ = P₁ · e^(−ΔH/R · (1/T₂ − 1/T₁)) relates two vapor pressures (P₁ and P₂) at different temperatures (T₁ and T₂). Here, ΔH is the enthalpy of vaporization (energy needed to turn liquid into gas), R is the gas constant (8.314 J/mol·K), and temperatures must be in Kelvin. The exponential term captures the relationship between temperature changes and vapor pressure, where a small temperature increase leads to a significant pressure rise due to the negative exponent and the positive ΔH value.

Practical Applications

This calculation is essential in engineering and chemistry for designing systems involving phase changes, such as distillation columns, refrigeration cycles, or chemical reactors. For example, knowing the vapor pressure at a new temperature helps determine the boiling point of a liquid under different pressures, ensuring safe operation in industries like oil refining or pharmaceuticals. It also aids in predicting how substances will behave in controlled environments, such as adjusting pressures in storage tanks to prevent leaks or explosions. Scientists use this tool to calibrate instruments and optimize experimental conditions for reactions requiring specific temperature and pressure ranges.

Day-to-Day Use

In everyday life, this concept explains why water boils faster at high altitudes, where lower atmospheric pressure reduces the boiling point. It's also relevant in cooking, like using pressure cookers to increase internal pressure and raise the boiling point of water, cooking food faster. In weather systems, vapor pressure helps predict cloud formation and precipitation by analyzing water vapor behavior. Additionally, understanding vapor pressure is crucial for maintaining household items like aerosol cans, which rely on controlled pressure to function safely, and in HVAC systems that regulate indoor humidity and temperature efficiently.

Worked example

Water at 350 K → ~41.5 kPa.

FAQ