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.
Latent heat of condensation (Lc): Refers to the heat gained by the air when water vapor changes into a liquid. Lc=2500 Joules per gram (J/g) of water or 600 calories per gram (cal/g) of water.
Latent heat of fusion (Lf): Refers to the heat lost or gained by the air when liquid water changes to ice or vice versa. Lf=333 Joules per gram (J/g) of water or 80 calories per gram (cal/g) of water.
Latent heat of sublimation (Ls): Refers to the heat lost or gained by the air when ice changes to vapor or vice versa. Ls=2833 Joules per gram (J/g) of water or 680 calories per gram (cal/g) of water.
Latent heat of vaporization (Lv): Refers to the heat lost by the air when liquid water changes into vapor. This is also commonly known as the latent heat of evaporation. Lv= -2500 Joules per gram (J/g) of water or -600 calories per gram (cal/g) of water.
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
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.