Heating curves, melting and boiling points
Answers are for parents and teachers.
1
Sketch a heating curve for water from −10 °C to 120 °C and label the five parts.
Rise (ice), flat at 0 °C (melting), rise (liquid), flat at 100 °C (boiling), rise (vapour).
2
Explain in your own words why the temperature stays constant while ice melts.
The energy is used to pull particles apart (potential energy), not to speed them up.
3
A substance melts at −20 °C and boils at 60 °C. State its state at −30, 0 and 80 °C.
Solid at −30 °C, liquid at 0 °C, gas at 80 °C.
4
Why does a pressure cooker help food cook faster?
Higher pressure raises the boiling point, so the water is hotter than 100 °C.
5
Find the mistake: “At 100 °C water boils everywhere on Earth.”
Only at normal sea-level pressure; on a mountain it boils at a lower temperature.