Latent Heat Calculator

Frequently Asked Questions

What is the difference between latent and sensible heat?

Latent heat drives a phase change at constant temperature, while sensible heat changes the temperature of a substance.

What are the latent heats of water?

The latent heat of fusion is about 334 kilojoules per kilogram and the latent heat of vaporization is about 2260 kilojoules per kilogram.

How do I calculate the heat for a phase change?

Multiply the mass by the specific latent heat: Q = m × L. For example, melting 2 kg of ice takes Q = 2 × 334 = 668 kJ. Use mass in kilograms and latent heat in kilojoules per kilogram so the units match.

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How This Calculator Works

Latent heat is the energy absorbed or released when a substance changes phase without changing temperature. The total heat equals the mass multiplied by the specific latent heat of the material. This is the energy needed to melt ice into water or to boil water into steam, separate from the energy that raises temperature.

Worked Example

How much energy does it take to melt 2 kg of ice at 0 °C into water at 0 °C? The specific latent heat of fusion of water is L = 334 kJ/kg. Using Q = m × L = 2 kg × 334 kJ/kg = 668 kJ, which is 668,000 J. Note the temperature never changes during melting; all 668 kJ goes into breaking the bonds of the solid structure rather than warming the water.

How To Use It

Enter the mass in kilograms and the specific latent heat in kilojoules per kilogram for the phase change you care about. For water, the latent heat of fusion is about 334 kilojoules per kilogram (melting at 0 °C) and the latent heat of vaporization is about 2260 kilojoules per kilogram (boiling at 100 °C). Both are standard-pressure (1 atmosphere) reference values and shift slightly at other pressures. The calculator returns the heat energy in kilojoules and in joules.

Other Substances and Sublimation

The same Q = m × L formula works for any material once you plug in its own specific latent heat. Typical standard-pressure reference values are:

Water: fusion 334 kJ/kg, vaporization 2260 kJ/kg

Ethanol: fusion about 108 kJ/kg, vaporization about 841 kJ/kg

Ammonia: vaporization about 1370 kJ/kg

Nitrogen: fusion about 25.7 kJ/kg, vaporization about 199 kJ/kg

Iron: fusion about 247 kJ/kg

Latent heat of sublimation applies when a solid turns straight into a gas without melting first, as dry ice (solid CO₂) does at about -78 °C. Its latent heat of sublimation is roughly 571 kJ/kg. For a substance that can sublime, the sublimation heat is close to the sum of its fusion and vaporization heats.

Sensible Versus Latent Heat

Sensible heat changes the temperature of a substance, while latent heat drives a phase change at constant temperature. Boiling water stays at one hundred degrees Celsius even as you keep adding energy, because that energy goes into breaking molecular bonds rather than warming the liquid.

Tips

Vaporization usually needs far more energy than melting.

Use mass in kilograms to match the kilojoule per kilogram unit.

Latent heat ignores any temperature change.

Latent Heat Calculator

Frequently Asked Questions

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