Boiling Point Calculator
Look up the boiling point of common substances at 1 atm, or calculate boiling points at different pressures using the Clausius-Clapeyron equation. Essential for laboratory work and cooking at altitude.
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What affects a liquid's boiling point?
Boiling point depends on intermolecular forces: stronger forces → higher boiling point. Hydrogen bonding (water, HF, ammonia) raises boiling points. Molecular weight also matters—heavier molecules need more energy to escape. Pressure: lower pressure = lower boiling point (why Mountains cooking takes longer). Purity: solutes raise boiling point; mixtures boil over a range.
How does pressure affect boiling point?
Lower pressure decreases boiling point; higher pressure increases it. At 1 atm, water boils at 100°C. At 0.5 atm (~5000 ft altitude), water boils at ~83°C. At 2 atm (pressure cooker), water boils at ~120°C. The Clausius-Clapeyron equation quantifies this relationship using heat of vaporization.
What is the heat of vaporization?
Heat of vaporization is energy required to convert 1 kg liquid to gas at its boiling point (no temperature change). For water at 100°C: 2257 kJ/kg. Higher heat of vaporization means more energy needed to boil. It decreases as temperature rises, reaching zero at the critical point.
Why does water have such a high boiling point?
Water's high boiling point (100°C vs -60°C for similar-size molecules) comes from hydrogen bonding. The strong H-bonds between water molecules require lots of energy to break. Ethanol (similar MW) boils at 78°C—lower than water because only one H-bond donor instead of two.
Can everything boil?
Every substance has a critical temperature above which it cannot be liquid—regardless of pressure. For water, this is 374°C and 218 atm. Above this, it's a supercritical fluid with properties between liquid and gas. Solid CO₂ sublimes at -78.5°C because triple point (where solid-liquid-gas meet) is at 5.1 atm—lower than atmospheric.