Calculators
Latent Heat Calculator
Solve phase-change energy with Q = mL.
Calculate energy transferred during a phase change, or rearrange Q = mL to solve mass or specific latent heat.
Calculated result
668 kJ
Q = mL
This model covers energy absorbed or released during an idealized phase change at approximately constant temperature. Use a specific-heat calculation separately for temperature changes before or after the phase change.
About This Tool
Latent heat is energy transferred when matter changes phase without the idealized phase-change temperature itself changing. The relation Q = mL connects heat energy Q, mass m, and specific latent heat L. This calculator solves any one of those quantities and handles common SI, calorie, and mass units for melting, freezing, vaporization, and condensation problems.
How To Use It
- Choose whether to solve heat energy, mass, or specific latent heat.
- Enter the two known quantities and select their units.
- Use the specific latent heat for the exact phase transition and material. Fusion and vaporization values for the same substance are different.
- If the material also changes temperature before or after its phase change, calculate that sensible heat separately with Q = mcΔT and combine the energy stages as needed.
Examples
Melting ice-style example
For 2 kg with L = 334 kJ/kg, Q = 668 kJ. This is the idealized phase-change energy only.
Using grams
For 500 g with L = 334 J/g, Q = 167 kJ.
Solve mass
If 668 kJ is transferred and L = 334 kJ/kg, the corresponding mass is 2 kg.
Solve latent heat
If 2 kg undergoes a phase change using 668 kJ, L = 334 kJ/kg.
Useful Notes
Latent heat formula
The phase-change relationship is Q = mL. Rearranging gives m = Q/L and L = Q/m. Specific latent heat is energy per unit mass, commonly expressed in J/kg or kJ/kg.
Fusion versus vaporization
Specific latent heat of fusion applies between solid and liquid phases. Specific latent heat of vaporization applies between liquid and gas phases. They are separate material properties and should not be substituted for one another.
Why temperature may stay constant
In the idealized model, energy transferred during a phase change changes molecular arrangement rather than temperature. Once the phase change is complete, additional energy can change temperature again.
Combine thermal stages carefully
A complete heating or cooling problem can include sensible-heating stages Q = mcΔT plus one or more phase-change stages Q = mL. Calculate each applicable stage and add their energy magnitudes for the full process.
Reference values are approximate
Published latent-heat values can vary with pressure, purity, and reference conditions. Use a reliable datasheet or handbook value appropriate to the problem instead of assuming a universal constant.
FAQ
What is the difference between specific heat and latent heat?
Specific heat relates energy to a temperature change using Q = mcΔT. Latent heat relates energy to a phase change using Q = mL, ideally without a temperature change during that transition.
Can this calculate melting and boiling?
Yes, if you supply the appropriate specific latent heat. Use latent heat of fusion for melting/freezing and latent heat of vaporization for boiling/condensation.
Why does the calculator not ask for temperature?
The basic Q = mL phase-change model does not use temperature change. Temperature changes outside the transition require separate sensible-heat calculations.
Can mass be zero?
A direct energy calculation with zero mass gives zero phase-change energy. Solving for specific latent heat requires a mass greater than zero because mass is the divisor.
Does pressure matter?
It can. Phase-change temperatures and latent heats can depend on pressure and material conditions. Use property data appropriate to the conditions when accuracy matters.
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