What Btu of heat is required to raise 1 pound of steam 1 degree F above the temperature of 212 degrees F?

• A. 0.25
• B. 0.75
• C. 1.0
• D. 0.5

Answer: (D)

Raising the temperature of steam uses its sensible heat, which is governed by the steam’s specific heat. For steam, the specific heat is about 0.5 Btu per pound per degree Fahrenheit. With 1 pound of steam and a temperature rise of 1°F (from 212°F to 213°F), the heat added is Q = m × cp × ΔT ≈ 1 × 0.5 × 1 = 0.5 Btu. This amount is only the energy to increase the temperature of already-formed steam; the large energy needed to form steam from liquid water (latent heat of vaporization) is separate and about 970 Btu per pound.