How many cubic feet of water vapor equals 1 pound?

Answer 1

Since water vapor is a gas, it depends on the Pressure and Temperature. The ideal gas law can be used for a given pressure and temperature. PV = nRT

Assuming 1 atmosphere pressure, and 100°C temperature (like the water had just boiled and turned to vapor, this can be computed. Note that water vapor can exist at a range of temperatures, not just above the boiling point. But at other temperatures, it will be mixed with the air (humidity).

1 pound = 453.59 grams. The Atomic Mass of H2O is 18 grams/mole, so 453.59 grams / (18 grams/mole) = 25.2 moles.

R is the ideal gas constant = 8.314472 Joule/Kelvin/mole. (SI units)

T of 100°C is 373 Kelvin. 1 atmosphere = 101325 pascals (SI unit equivalent to Joule/meter3).

Substituting these in and isolating V = 0.77129 cubic meters = 27.24 cubic feet.