Latent Heat Calculator

The latent heat equation is:

$$Q = m \cdot L$$

where Q is the heat energy (J), m is the mass (kg), and L is the specific latent heat of the transition (J/kg). There are two main types:

$$L_f = \text{latent heat of fusion (solid} \leftrightarrow \text{liquid)}$$

$$L_v = \text{latent heat of vaporization (liquid} \leftrightarrow \text{gas)}$$

For water, L_f = 334,000 J/kg at 0 °C and L_v = 2,260,000 J/kg at 100 °C. Notice that vaporization requires roughly 6.8 times more energy than fusion—breaking intermolecular bonds completely to form a gas demands far more energy than merely loosening them to form a liquid.

This explains why steam burns are far more dangerous than boiling-water burns: condensing steam releases 2.26 MJ per kilogram onto your skin in addition to the heat of the hot water itself.

The calculated Q represents the total energy exchanged during the phase change at constant temperature. This energy goes entirely into changing the molecular arrangement, not the kinetic energy (temperature) of the molecules.

For practical applications: to melt 1 kg of ice at 0 °C you need 334 kJ, but to then heat that water from 0 °C to 100 °C you need an additional 418.6 kJ (using Q = mcΔT), and to boil it requires yet another 2260 kJ. The vaporization step dominates the total energy budget.