Interconversions between the three states of matter
3 marks · NormalA student heats 10 g of solid iodine in a sealed container. The iodine sublimes completely, forming a gas. The total mass of the container and its contents does not change during this process.
State the process that occurs when solid iodine changes directly into a gas.
Explain, using particle theory, why the mass of the container and its contents does not change when the solid turns into a gas. Include ideas about particles and their arrangement.
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Show answer
(a) Sublimation
(b) — · must show Explanation that mass is conserved because the number of particles does not change, only their arrangement and movement changes, Reference to sealed container preventing loss of particles
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Marking points
B1 (a) · 1 mark · States that the process is sublimation.
B2 (b) · 1 mark · Explains, using particle theory, that the particles are the same before and after the change—no gain or loss of particles.
B3 (b) · 1 mark · Mentions that the container is sealed so no particles can leave or enter, keeping the mass constant.
Worked solution
a) The process is called sublimation.
b) The mass of the container and its contents does not change because the number of particles remains the same—the iodine particles simply gain energy and move from a solid arrangement to a gas arrangement. In a sealed container, none of the particles can escape, so no mass is lost or gained.