Approximately how many BTU are required to vaporize one pound of water?

Approximately how many BTU are required to vaporize one pound of water?

• A. 980 BTU per pound
• B. 520 BTU per pound
• C. 400 BTU per pound
• D. 1100 BTU per pound

Answer: (A)

This question tests the energy needed to change water from liquid to steam at its boiling point, which is the latent heat of vaporization. For water at 100°C (212°F), the latent heat of vaporization is about 970 BTU per pound. So, about 980 BTU per pound is the best match. That energy is required without raising the temperature, to overcome the molecular bonds as water becomes steam. The other numbers are either too low or a bit high for this phase change energy, so they don’t align with the standard value as closely.

This question tests the energy needed to change water from liquid to steam at its boiling point, which is the latent heat of vaporization. For water at 100°C (212°F), the latent heat of vaporization is about 970 BTU per pound. So, about 980 BTU per pound is the best match. That energy is required without raising the temperature, to overcome the molecular bonds as water becomes steam.

The other numbers are either too low or a bit high for this phase change energy, so they don’t align with the standard value as closely.