How many BTUs are required to change one pound of ice to water?

How many BTUs are required to change one pound of ice to water?

• A. 10 BTUs
• B. 144 BTUs
• C. 970 BTUs
• D. 70 BTUs

Answer: (B)

Melting ice requires the latent heat of fusion—the energy needed to change a solid to a liquid at the melting point. For ice at 0°C turning into water at 0°C, this energy is 144 BTU per pound. It’s the amount absorbed without a temperature change during the phase transition. The other values correspond to different processes: 970 BTU is the energy to vaporize water (liquid to steam), not melt ice; 10 and 70 BTU are far too small to cause melting. So the correct amount is 144 BTU per pound.

Melting ice requires the latent heat of fusion—the energy needed to change a solid to a liquid at the melting point. For ice at 0°C turning into water at 0°C, this energy is 144 BTU per pound. It’s the amount absorbed without a temperature change during the phase transition. The other values correspond to different processes: 970 BTU is the energy to vaporize water (liquid to steam), not melt ice; 10 and 70 BTU are far too small to cause melting. So the correct amount is 144 BTU per pound.