How many Btu's are necessary to change 1 pound of water at 212F into 1 pound of steam at 0 psig?

To determine how many Btu's are necessary to convert 1 pound of water at 212°F into 1 pound of steam at 0 psig, it is important to understand the processes involved in this phase change.

At 212°F, water is at its boiling point under normal atmospheric pressure. To convert the water into steam, you need to provide enough heat energy to not only bring the water to its boiling point (which it already is) but also to supply the latent heat of vaporization. The latent heat of vaporization is the amount of energy required to convert a unit mass of a substance from liquid to vapor without a change in temperature.

For water, the latent heat of vaporization is approximately 970.3 Btu per pound. This means that to change 1 pound of water at 212°F into 1 pound of steam under atmospheric pressure, you would require 970.3 Btu of energy.

This process does not require additional energy for heating past the boiling point since the water is already at 212°F. The energy input required is solely to achieve the phase change from liquid to gas, represented by the heat of vaporization.

Hence, the correct answer of 970.3 Btu accurately reflects the