Boiling Point Calculator

A liquid boils when its vapor pressure equals the pressure surrounding it. The familiar boiling point listed in reference tables is usually the normal boiling point, measured at one atmosphere. It is not a fixed temperature under every condition. Lowering external pressure lets molecules escape into the vapor phase at a lower temperature, while raising pressure requires a higher temperature. This is why water boils below 100 °C at high altitude and why a pressure cooker operates above 100 °C. This boiling point calculator estimates that pressure-dependent change with the integrated Clausius-Clapeyron equation. It uses a known boiling temperature and pressure as a reference, then combines them with the target pressure and molar enthalpy of vaporization. All temperatures are converted internally to kelvin, and enthalpy entered in kilojoules per mole is converted to joules per mole so it is compatible with the universal gas constant. Pressure units cancel in the ratio, but both pressure entries must use the displayed unit consistently. The method assumes the vapor behaves approximately as an ideal gas, the liquid's molar volume is small compared with the vapor volume, and enthalpy of vaporization remains constant across the temperature interval. Those assumptions are useful over modest pressure and temperature ranges. Accuracy declines near the critical point, across a phase transition, or when the target pressure is far from the reference pressure. For engineering design, safety calculations, or highly nonideal mixtures, use measured vapor-pressure data or a suitable equation of state. Choose reliable input data for the substance and temperature range of interest. Enthalpy of vaporization varies with temperature and approaches zero near the critical point, so a value measured close to the reference boiling point gives the best estimate. For mixtures, composition changes as boiling proceeds and a single pure-component calculation may not describe bubble and dew points. Even with those limitations, the calculator provides a transparent and quick estimate for laboratory planning, altitude comparisons, vacuum evaporation, distillation studies, and chemistry homework.