How many BTUs are required to change one pound of water at 212 F to a vapor?

How many BTUs are required to change one pound of water at 212 F to a vapor?

• A. 970 BTUs
• B. 540 BTUs
• C. 800 BTUs
• D. 1000 BTUs

Answer: (A)

This question tests understanding of the latent heat of vaporization—the energy needed to turn a liquid into vapor at its boiling point without changing its temperature. For water boiling at 212 F (100 C), the latent heat of vaporization is about 970 BTU per pound. So, to convert one pound of water at boiling to steam, you must supply roughly 970 BTUs, which makes that option the correct one. The other numbers don’t match the known latent heat of vaporization for water at the boiling point.

This question tests understanding of the latent heat of vaporization—the energy needed to turn a liquid into vapor at its boiling point without changing its temperature. For water boiling at 212 F (100 C), the latent heat of vaporization is about 970 BTU per pound. So, to convert one pound of water at boiling to steam, you must supply roughly 970 BTUs, which makes that option the correct one. The other numbers don’t match the known latent heat of vaporization for water at the boiling point.