Reversible changes, sublimation and evaporation
Answers are for parents and teachers.
1
Make a table: melting, boiling, freezing, condensation. For each give from → to and whether heat is gained or lost.
Melting solid → liquid, gained; boiling liquid → gas, gained; freezing liquid → solid, lost; condensation gas → liquid, lost.
2
Explain why washing dries faster on a breezy day.
Moving air carries the water vapour away, so more water can evaporate.
3
A friend says that boiling is just very fast evaporation. Explain what is wrong.
They are different: boiling is at the boiling point, through the whole liquid, with bubbles; evaporation is only at the surface.
4
Is dissolving sugar in tea a change of state? Is it physical or chemical?
It is not a change of state; it is a physical change, because the sugar can be recovered.
5
Find the mistake: “The drops on a cold glass came through the glass.”
They come from water vapour in the air that condensed on the cold glass.