The phase changes of water

Water can exist in all three phases at temperatures commonly found in the atmosphere. In many instances, water changes from one phase to another. In changing from one phase to another, water either absorbs or releases energy into the air. This hidden energy is commonly referred to as latent heat. The three basic types of latent heat are as follows.

The following table shows the six phase change processes that water can undergo and the heat gained or lost by the air in each of the processes.

Process                 Changes           Heat gained or lost by the air

                          From             To

Condensation    vapor          liquid        2500 J/g or 600 cal/g

Deposition        vapor          ice           2833 J/g or 680 cal/g

Evaporation       liquid         vapor        -2500 J/g or -600 cal/g

Freezing           liquid         ice           333 J/g or 80 cal/g

Melting            ice            liquid       -333 J/g or -80 cal/g

Sublimation      ice            vapor        -2833 J/g or -680 cal/g

To convert the figures above to British Thermal Units (BTUs), you can use 1 BTU equals 1055 jules or 1 BTU equals 252 calories. To convert grams to ounces, use 1 ounce equals 28.35 grams. A pound equals 16 ounces. Ounces and pounds are not units of mass, but are often used this way.

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