During boiling, how does the temperature of the liquid change as heat is added?

During boiling, how does the temperature of the liquid change as heat is added?

• A. It rises
• B. It stays constant
• C. It falls
• D. It becomes superheated

Answer: (B)

During boiling, added heat goes into turning the liquid into gas rather than raising its temperature. This uses the latent heat of vaporization, and at a fixed pressure the boiling point stays the same. So, as long as some liquid remains, its temperature remains constant (for water at 1 atm that’s 100°C). Only after all the liquid has vaporized does further heating raise the temperature of the steam.

During boiling, added heat goes into turning the liquid into gas rather than raising its temperature. This uses the latent heat of vaporization, and at a fixed pressure the boiling point stays the same. So, as long as some liquid remains, its temperature remains constant (for water at 1 atm that’s 100°C). Only after all the liquid has vaporized does further heating raise the temperature of the steam.