Interconversions between the three states of matter
3 marks · NormalAmmonium chloride can change directly from a solid to a gas when heated. Explain why the process observed is called sublimation, and describe what happens to the particles during this process.
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Also accept: Sublimation is the direct change from solid to gas without forming a liquid. During this process, the particles gain enough energy to move from a closely packed arrangement to being far apart and moving rapidly in all directions, as in a gas.
Common mistakes: Saying it goes through a liquid stage
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Marking points
M1 · 1 mark · States that sublimation is the direct change from solid to gas (without becoming liquid).
M2 · 1 mark · Describes that during sublimation, particles gain enough energy to overcome forces holding them in solid.
A1 · 1 mark · Describes the resulting particle arrangement: far apart, randomly moving (as in a gas).
Worked solution
Sublimation is the direct change from a solid to a gas, without the substance becoming a liquid.
In this process, the particles in solid ammonium chloride gain enough energy to overcome the strong forces holding them close together.
As a result, the particles become far apart and move at high speeds randomly, as in a gas.