O-LevelPhysicsThermal Physics5054/22 · May/June 2017 · Q56 Marks

When a sample of a solid is heated, it becomes a liquid and eventually becomes a gas. Fig. 5.1 shows the arrangement of the molecules in the solid. [Figure 5.1]

(a)In the space below, draw the arrangement of the molecules in the liquid.[1]
(b)Complete the table by describing the motion of the molecules in the solid, liquid and gas.[3]
(c)Suggest why a gas is able to fill a container but a solid has a fixed shape.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] irregular arrangement of at least 8 molecules with at least one molecule touching other
[1] solid - vibrate (about fixed positions)
[1] liquid - change position / slide (over each other) or move / translate throughout (liquid) or move in clusters
[1] gas - random movement or move in all directions or high speed / kinetic energy or have range of speeds or move throughout container or move in a straight line (between collisions) or move freely
[1] no/weak force between molecules in gases or molecules not held together in gases
[1] speed/K.E of gas molecules fast(er) than solids

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