A-LevelPhysicsThermodynamics9702/41 · Oct/Nov 2018 · Q29 Marks
An ideal gas undergoes a cycle of changes as shown in [Figure 2.1]. At point P, the gas has volume 950 cm³, pressure 2.10 × 10⁵ Pa and temperature 280 K. The gas is heated at constant volume and 97.0 J of thermal energy is transferred to the gas. Its pressure and temperature change so that the gas is at point Q on Fig. 2.1. The gas then undergoes the change from point Q to point R and then from point R back to point P, as shown on Fig. 2.1.
- (a)State what is meant by the internal energy of a system.[2]
- (b)(i)State the total change in internal energy of the gas during the complete cycle PQRP. Explain your answer.[2]
- (b)(ii)On [Figure 2.2], complete the energy changes for the gas during 1. the change P → Q, 2. the change Q → R, 3. the change R → P.[5]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [B1] sum of potential and kinetic energies (of molecules/atoms/particles)
- [B1] (energy of) molecules/atoms/particles in random motion
- [B1] final temperature = initial temperature
- [B1] no change in internal energy
- [A1] 1. work done on gas (P→Q): 0
- [A1] increase in internal energy (P→Q): (+)97.0J
- [A1] 2. increase in internal energy (Q→R): -42.5J
- [A1] 3. increase in internal energy (R→P): -54.5J
- [A1] thermal energy supplied (R→P): -91.5J
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