Heat of fusion and vaporisation
Answers are for parents and teachers.
1
How many J of heat are needed to melt 1.5 kg of ice at 0 °C (λ = 336 000 J/kg)?
504000
2
How many J are needed to vaporise 3 kg of water at 100 °C (r = 2 300 000 J/kg)?
6900000
3
1 kg of ice at 0 °C becomes water at 0 °C and then 10 °C. Find the total heat (c = 4200).
1·336 000 + 1·4200·10 = 378 000 J
4
Why does a sweating person feel cooler in the wind on a hot day?
Wind speeds up evaporation, and evaporation cools the body.
5
Why does the temperature of boiling water not rise when the gas flame is increased?
The extra energy goes into vaporising water, so the temperature stays at 100 °C.