Latent Heat Calculator
Calculate the energy needed to melt, freeze, boil or condense a substance using Q = m times L. A phase change happens at constant temperature, so only mass and the specific latent heat matter.
How to calculate latent heat
- Enter the mass of the substance in kilograms.
- Enter the specific latent heat L in joules per kilogram.
- Use fusion for melting or freezing, and vaporization for boiling or condensing.
- Read the energy in joules and kilojoules.
Examples
Melt 0.5 kg of ice
m = 0.5 kg, L = 334000 J/kg (fusion)
Q = 167000 J = 167 kJ
Boil 1 kg of water
m = 1 kg, L = 2256000 J/kg (vaporization)
Q = 2256000 J = 2256 kJ
Frequently asked questions
What is the latent heat formula?
Q = m * L, where Q is the heat in joules, m is the mass in kilograms and L is the specific latent heat in joules per kilogram. The temperature stays constant during the phase change.
What is the difference between fusion and vaporization?
Latent heat of fusion is the energy to melt or freeze a substance. Latent heat of vaporization is the energy to boil or condense it, and it is usually much larger.
What are common latent heat values for water?
Water has a latent heat of fusion near 334000 J/kg (334 kJ/kg) and a latent heat of vaporization near 2256000 J/kg (2256 kJ/kg) at standard pressure.
What about other substances?
Useful values include about 205000 J/kg fusion for ethanol, 871000 J/kg vaporization for ethanol, and 24500 J/kg fusion plus 858000 J/kg vaporization for lead.
Does temperature change during a phase change?
No. While a substance is melting or boiling, added heat goes into the phase change and the temperature stays constant. Use a specific heat calculator for heating within one phase.
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