Latent Heat Calculator

The latent heat calculator helps you compute the energy released or absorbed during a phase transition like melting or vaporizing. In the text below, we explain what is specific latent heat and present a simple latent heat calculation.

Specific latent heat is energy hidden in the internal structure of a substance. As we saw in the sensible heat calculator, if we transfer heat to water, its temperature increases according to its specific heat.

Once the temperature reaches the boiling point, something interesting happens. The temperature stops increasing, and instead, the water vaporizes. This process of turning water into vapor takes some energy. This is the latent heat. Once all the water is turned into vapor, a further transfer of heat will simply increase the temperature again.

Condensation is the reverse process of vaporization, where gas turns into liquid. The latent heat released during condensation is equal to the latent heat absorbed during vaporization.

A change from a liquid to a gaseous phase is an example of a phase transition. Another common phase transition is from a solid to a liquid phase. Specific latent heat is the amount of energy absorbed or released during the phase transition per 1 kg of the substance.

All we need to know to compute the latent heat is the amount of substance and its specific latent heat. The formula is:

where:

• $m\ \rm [kg]$ — Mass of the body;
• $L\ \rm [kJ/kg]$ — Specific latent heat; and
• $Q\ \rm [kJ]$ — Heat absorbed or released depending on the direction of the transition.

The specific latent heat is different for solid-to-liquid transition and liquid-to-gas transition. For example, if we want to turn $\small 20\ \rm g$ of ice into water, we need $\small Q = 20\ \rm g \times 334\ kJ/kg = 6680\ J$ of energy. To turn the same amount of water into vapor, we need $\small Q = 45294\ \rm J$.

Our calculator makes the computation of latent heat simple. It provides the specific latent heat for a few substances. If the substance that you're after is not on the list, just select the Other option and input your own specific latent heat below it.

It's amusing to observe that it takes less energy to go from solid-state to liquid phase than to go from liquid phase to gas. It means that liquids are more like solids than gases.