A pot of water is boiling vigorously at 100°C. You turn up the burner to maximum. What happens to the water temperature?
AIt rises above 100°C immediately
BIt stays at 100°C until all the water has evaporated
CIt fluctuates between 95°C and 105°C
DIt drops slightly due to increased evaporation cooling
At 1 atm, water's boiling point is 100°C. During boiling, all added heat goes into the latent heat of vaporization — breaking the intermolecular bonds in the liquid — rather than raising the temperature. The water cannot rise above 100°C until the last drop of liquid has converted to steam. Turning up the burner only makes water boil faster, not hotter.
Question 2 True / False
Evaporation and boiling are essentially the same process and occur under the same conditions.
TTrue
FFalse
Answer: False
Evaporation occurs at any temperature from the liquid's surface, driven by the fastest-moving surface molecules escaping into the vapor phase. Boiling requires reaching the boiling point and occurs throughout the bulk liquid, forming bubbles that rise to the surface. A wet shirt dries by evaporation at room temperature — that is not boiling.
Question 3 Short Answer
During melting, a solid absorbs heat but its temperature does not rise. Where does that energy go?
Think about your answer, then reveal below.
Model answer: The energy goes into breaking the intermolecular bonds that hold molecules in the rigid lattice structure of the solid, converting it to the less-ordered liquid phase — not into increasing molecular kinetic energy.
Temperature is a measure of average kinetic energy. During a phase transition, the added heat (called latent heat) disrupts the ordered structure rather than speeding molecules up. Once the transition is complete, further heating resumes raising the temperature. This is why the temperature-vs-time graph is flat during melting and boiling.