What is the latent heat of vaporization?

It is the amount of energy per unit mass needed to convert a substance from liquid to gas at its boiling point, without changing temperature. It is measured in J/g or kJ/kg.

What does Q = m × L mean?

Q is the total heat energy required, m is the mass of the substance, and L is the specific latent heat of vaporization. The result is in joules when m is in grams and L is in J/g.

Why does temperature stay constant during vaporization?

The energy added goes entirely into breaking the intermolecular bonds of the liquid rather than raising its temperature, so the temperature stays at the boiling point until all the liquid has vaporized.

Does pressure affect the latent heat?

Yes. The values in this calculator are at standard atmospheric pressure (1 atm). At higher pressures the boiling point rises and latent heat values change slightly.

Can I enter a custom latent heat value?

Yes. Select "Custom" from the substance list and type the latent heat in J/g directly.

Heat of Vaporization Calculator

Enter a mass and choose a substance to calculate the heat energy needed to completely vaporize it using Q = m × L.

Inputs

Mass

Substance

Boiling point (1 atm): 100 °C | Latent heat: 2260 J/g

Results

Enter a mass and click Calculate.

Copied!

Summary

This calculator uses the formula Q = m × L to find the heat energy needed to vaporize a given mass of substance. You supply the mass and select a substance; the tool looks up its latent heat of vaporization (L) and computes the energy in joules, kilojoules, and kilocalories. All calculations run entirely in your browser.

How it works

Enter the mass of the substance you want to vaporize.
Select the unit for mass: grams, kilograms, or pounds.
Choose a preset substance or enter a custom latent heat value.
The calculator multiplies mass × latent heat to compute Q.
Results are shown in joules, kilojoules, and kilocalories.

Use cases

Solve thermodynamics homework problems involving phase changes.
Estimate the energy cost of evaporating water in industrial processes.
Compare how much energy different substances need to vaporize.
Verify manual Q = mL calculations instantly.
Study the relationship between latent heat and boiling energy.
Engineering design: size a boiler or heat exchanger correctly.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu