How to Calculate the Heat Released From 100 Degrees of Steam to Water at 100 Degrees

Steam condenses into water inside a radiator, releasing heat into the room.

Whenever any material undergoes a phase change, such as boiling or melting, heat energy is either absorbed or released without affecting the overall temperature of the material. When a liquid turns into a gas by boiling, or a gas condenses into a liquid, the amount of energy involved is called the latent heat of vaporization, which varies from substance to substance. For a solid melting into a liquid or a liquid freezing into a solid, it's the latent heat of fusion.

Things You'll Need

• Table of Latent Heats
• Calculator (optional)

Instructions

1. Look up the latent heat of vaporization for the substance in question. Here we are dealing with water, which has a latent heat of vaporization of 2258 kJ/kg, or 970.4 BTU/lb.

2. Determine how much steam is condensing into water, if it is not already specified in the problem. Since liquid water has a density of 958 grams per liter at 100 degrees Celsius, you can measure by weight or volume and convert as necessary.

3. Multiply the mass of water in kilograms by 2258 kJ/kg (the latent heat of vaporization of water) to get the amount of energy in kilojoules released when that water condenses out of steam. If you prefer to work in imperial measurements, multiply the weight of the water in pounds by 970.4 BTU/lb to get the answer in BTUs.

Tips & Warnings

• You can perform this calculation in either direction: figure out how much water you can boil with a given amount of energy, figure out how much steam you need to condense to release a given amount of energy, and so on.

• Boiling water can burn you badly, and steam can be even worse. Exercise caution if you need to physically measure either.

References

• Splung: Latent Heat
• Engineering Toolbox: Fluids - Latent Heat of Evaporation