Physics 5054 · O Level · Particle model

Particle model — practice question

A gas is enclosed in a cylinder by a piston while under atmospheric pressure. A movable rod keeps the piston in a fixed position. Figure 6.1 shows the cylinder. The cylinder is heated. As the gas temperature rises, the pressure rises as well.
(a)[2]

Explain, in molecular terms, why the pressure of the trapped gas rises.

(b)[3]

The rod is pulled down, after which the piston can move freely, as shown in Fig. 6.2. While the piston moves, the gas temperature stays constant. State and explain, in molecular terms, what happens to the gas pressure.

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This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Molecules move more quickly / gain kinetic energy” …

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