States of Matter
5 marks · EasyA scientist describes placing solid iodine in an open dish in a laboratory. After a few hours, no solid remains, and a purple vapour fills the dish.
Describe the arrangement and movement of particles in solid iodine at room temperature.
Identify the name of the process that causes solid iodine to disappear and form a vapour.
Explain, using particle theory, what happens to the particles of iodine during this process.
State one difference between the arrangement of particles in the iodine vapour and in the solid.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Particles are closely packed in a regular arrangement and can only vibrate about fixed positions.
(b) Sublimation
(c) Particles gain energy and leave their fixed positions. They move apart and randomly in all directions, forming a gas/vapour.
(d) In the vapour, particles are far apart and randomly arranged; in the solid, they are close together and regularly arranged.
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Marking points
B1 (a) · 1 mark · States particles are closely packed in a regular arrangement and only vibrate.
B1 (b) · 1 mark · Correctly names the process as 'sublimation'.
M1 (c) · 1 mark · Mentions particles gain energy and leave their fixed positions (or break free).
A1 (c) · 1 mark · Describes that the particles move far apart and at random (forming a gas/vapour).
B1 (d) · 1 mark · States a key difference in arrangement between vapour and solid (random and far apart in vapour, regular and close in solid).
Worked solution
a) In solid iodine, the particles are closely packed in a regular arrangement and can only vibrate about fixed positions.
b) The process is called sublimation.
c) During sublimation, the particles in the solid gain energy and overcome their forces of attraction. They break away from their fixed positions, move far apart, and move randomly in all directions as a vapour.
d) In the vapour, the particles are much further apart and arranged randomly, whereas in the solid they are close together and arranged regularly.