The first law of thermodynamics can be represented by the expression ΔU = q + w. (b) A fixed mass of an ideal gas undergoes a cycle ABCA of changes, as shown in Fig. 2.1. 6.0 pressure/10⁵ Pa A 5.0- 4.0- 3.0- 2.0- 1.0- B C 0+ 0 2.0 4.0 6.0 volume/10⁻⁴ m³ Fig. 2.1

1. (a)State what is meant by the symbols in the expression. +ΔU +q +w[2]
2. (b)(i)During the change from A to B, the energy supplied to the gas by heating is 442 J. Use the first law of thermodynamics to show that the internal energy of the gas increases by 265 J.[2]
3. (b)(ii)During the change from B to C, the internal energy of the gas decreases by 313 J. By considering molecular energy, state and explain qualitatively the change, if any, in the temperature of the gas.[3]
4. (b)(iii)For the change from C to A, use the data in (b)(i) and (b)(ii) to calculate the change in internal energy.[1]
5. (b)(iv)The temperature of the gas at point A is 227 °C. Calculate the number of molecules in the fixed mass of the gas.[2]

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.