When water freezes at 32°F, how much heat is lost per pound of water?

• A. 32 BTU
• B. 72 BTU
• C. 144 BTU
• D. 200 BTU

Answer: (C)

The correct answer, which indicates that the heat lost per pound of water when it freezes is 144 BTU, is based on the principle of latent heat. When water transitions from a liquid state to a solid state (freezing), it releases latent heat.

Specifically, the latent heat of fusion for water is approximately 144 BTUs per pound. This means that when one pound of water freezes, it releases 144 BTUs of energy to the surroundings. This energy release is critical in maintaining temperature stability in natural and artificial environments.

The other values represented in the options do not match the established latent heat of fusion for water: 32 BTUs is insufficient for the phase change, and 72, 200 BTUs are both misrepresentations of how much energy is lost during the freezing process. Thus, the accepted value of 144 BTUs accurately reflects the thermodynamic principles governing the phase transition of water from liquid to solid.