Latent Heat Calculator

Latent heat is the energy absorbed or released during a phase change at constant temperature. Melting 1 kg of ice requires 334 kJ regardless of how fast it melts.

🌡️ Thermodynamics📐 Q = mL💧 Phase Changes
Mass m (kg)
Latent Heat L (J/kg)

Ice melting: 334,000 J/kg  |  Water boiling: 2,260,000 J/kg

Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
Heat EnergyQQ = mLJ
Massmm = Q/Lkg
Latent HeatLL = Q/mJ/kg
Water fusionLf334,000 J/kgJ/kg
Water vaporizationLv2,260,000 J/kgJ/kg

Step-by-Step Examples

Example 1
Melting Ice

Melt 5 kg of ice. L = 334,000 J/kg.

  • Q = mL = 5 * 334,000 = 1,670,000 J
✓ 1,670 kJ to melt 5 kg of ice
Example 2
Boiling Water

Vaporize 2 kg of water. L = 2,260,000 J/kg.

  • Q = 2 * 2,260,000 = 4,520,000 J = 4520 kJ
✓ 4520 kJ — nearly 4x more than heating water from 0 to 100 deg C
Example 3
Steam Condensation

0.5 kg of steam condenses.

  • Q = 0.5 * 2,260,000 = 1,130,000 J released
  • Condensation releases the same heat as vaporization
✓ 1130 kJ released — why steam burns are severe

Real-World Applications

🧊
Refrigeration
Evaporating refrigerant absorbs latent heat from inside the fridge, cooling it.
☔
Climate Regulation
Ocean evaporation and rainfall release/absorb enormous latent heat, driving weather.
🏭
Industrial Drying
Removing moisture from food, paper, or chemicals requires supplying latent heat of vaporization.
🌡️
Thermal Energy Storage
Phase-change materials (PCMs) store large energy at near-constant temperature.

Common Mistakes to Avoid

⚠️
Latent heat vs sensible heat

Sensible heat (Q = mc*dT) changes temperature. Latent heat changes phase at constant temperature. Both may apply in sequence.

⚠️
Fusion vs vaporization values

Water: L_fusion = 334 kJ/kg (melting), L_vaporization = 2260 kJ/kg (boiling). They are very different.

⚠️
Direction matters

Melting and vaporization absorb heat. Freezing and condensation release the same amount.

Frequently Asked Questions

Why does temperature stay constant during phase change? ▾
All energy input goes into breaking intermolecular bonds, not increasing kinetic energy. Once the phase change is complete, temperature rises again.
Why is latent heat of vaporization so large? ▾
Vaporization completely separates molecules, breaking all intermolecular forces. Melting only partially disrupts the solid lattice.
How does sweating cool the body? ▾
Sweat evaporation absorbs ~2430 J/g from the skin via latent heat of vaporization, removing heat without raising skin temperature.
What are phase change materials (PCMs)? ▾
Substances that melt/freeze at useful temperatures (e.g. 20-25 deg C), storing large amounts of energy in building walls or cooling vests.
Does pressure affect latent heat? ▾
Yes. At higher pressures, boiling point rises and L_v changes. At lower pressures (high altitude), water boils at lower temperature with slightly different L_v.

Related Physics Calculators

🌡️ Specific Heat🔥 Heat Conduction⚙️ Carnot Efficiency🌡️ Thermal Expansion💨 Ideal Gas Law

Formula Explorer connections

Interpretation: This formula tracks heat, temperature, work, entropy or transport in a thermodynamic system. Assumption: Use absolute temperature where required and consistent energy units. Constant properties, equilibrium, ideal gases or negligible losses may be assumed.

Specific Heat Calculator →Specific Heat Ratio Calculator →Stefan-Boltzmann Law Calculator →Physics Formula Explorer →