To convert 5 lb of ice at 32°F to water, how much heat is required?

To determine the amount of heat required to convert ice at 32°F to water at the same temperature, we need to consider the latent heat of fusion. The latent heat of fusion is the amount of heat needed to change a substance from a solid to a liquid at constant temperature. For water, this value is approximately 144 BTU per pound.

Given that there are 5 pounds of ice, the total heat required can be calculated using the formula:

Heat required = Mass of ice × Latent heat of fusion.

Substituting the known values into the formula:

Heat required = 5 lb × 144 BTU/lb = 720 BTU.

This calculation confirms that to convert 5 lb of ice at 32°F to water, you would need a total of 720 BTUs. This is why the answer is considered correct.

The choices that represent lower values do not account for the correct amount of energy necessary for the phase change, while also ensuring that it is understood that the latent heat is critical in determining the required heat for this transition.