A Level Physics (A2) chapter 5: Thermodynamics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
48 exam-style questions on Thermodynamics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A gas in a well-insulated cylinder is compressed quickly, so that no energy is transferred by heating. 80 J of work is done on the gas. Which statement is correct?
A
its internal energy increases by 80 J and its temperature rises
B
its internal energy decreases by 80 J and its temperature falls
C
its internal energy is unchanged, because it has not been heated
D
its internal energy increases by 80 J but its temperature does not change
Show answer
Answer: A. q = 0 and W = +80 J, so ΔU = +80 J. For a gas, a rise in internal energy means a rise in the mean kinetic energy of the molecules, so the temperature rises.
2. Sample A is 2.0 mol of a monatomic ideal gas at 300 K. Sample B is 3.0 mol of the same gas at 400 K. What is (internal energy of B) ÷ (internal energy of A)?
A
0.50
B
1.3
C
1.5
D
2.0
Show answer
Answer: D. U = 3/2 nRT, so U ∝ nT: the ratio is (3.0 × 400)/(2.0 × 300) = 2.0. Comparing only the temperatures gives 1.3; only the amounts gives 1.5.
3. An ideal gas at a constant pressure of 1.5 × 105 Pa has a volume of 2.0 × 10−3 m3 at 300 K. It is heated to 450 K at the same pressure. How much work does the gas do?
A
100 J
B
150 J
C
300 J
D
450 J
Show answer
Answer: B. V ∝ T at constant pressure, so the new volume is 3.0 × 10−3 m3 and W = pΔV = 1.5 × 105 × 1.0 × 10−3 = 150 J. 450 J uses the whole final volume instead of the change.
4. A gas is taken once round a cycle and returns to its original state. During the cycle it receives 900 J by heating and loses 600 J by heating. What is the total work done on the gas during the cycle?
A
+300 J
B
+1500 J
C
−300 J
D
zero
Show answer
Answer: C. Over a complete cycle ΔU = 0, so W = −q = −(900 − 600) = −300 J. The negative sign shows that the gas does 300 J of work on its surroundings, as in a heat engine.
5. A gas expands at a constant pressure of 2.0 × 105 Pa from a volume of 1.5 × 10−3 m3 to 4.0 × 10−3 m3. How much work is done by the gas?
A
500 J
B
800 J
C
300 J
D
1100 J
Show answer
Answer: A. W = pΔV = 2.0 × 105 × (4.0 − 1.5) × 10−3 = 500 J. Only the change in volume counts, not the initial or the final volume on its own.
6. A gas expands at a constant pressure of 1.0 × 105 Pa from 2.0 × 10−3 m3 to 5.0 × 10−3 m3 while 750 J of energy is supplied to it by heating. What is the increase in its internal energy?
A
1050 J
B
750 J
C
300 J
D
450 J
Show answer
Answer: D. Work done on the gas W = −pΔV = −1.0 × 105 × 3.0 × 10−3 = −300 J, so ΔU = q + W = 750 − 300 = 450 J. Part of the energy supplied is used to push back the surroundings.
7. 1 kg of water at 100 °C and 1 kg of steam at 100 °C are compared. Which statement is correct?
A
the steam has more internal energy, because its molecules have more potential energy
B
they have the same internal energy, because they are at the same temperature
C
the water has more internal energy, because its molecules are closer together
D
the steam has more internal energy, because its molecules have a greater mean kinetic energy
Show answer
Answer: A. At the same temperature the mean molecular kinetic energy is the same. The steam has absorbed the latent heat of vaporisation, which raised the potential energy of its widely separated molecules, so its internal energy is greater.
8. A gas is compressed at a constant pressure of 1.2 × 105 Pa, and its volume decreases by 300 cm3. What is the value of W in ΔU = q + W?
A
−36 J
B
+36 J
C
+3.6 × 107 J
D
−3.6 × 107 J
Show answer
Answer: B. ΔV = 300 cm3 = 3.0 × 10−4 m3, so pΔV = 1.2 × 105 × 3.0 × 10−4 = 36 J. Work is done on the gas when it is compressed, so W is positive.
9. A gas is taken through a series of changes and returns to its original pressure, volume and temperature. Which statement must be correct?
A
the total work done on the gas is zero
B
the total energy supplied to the gas by heating is zero
C
its internal energy is the same as at the start
D
its internal energy has increased by the total work done on it
Show answer
Answer: C. Internal energy is determined by the state of the system, so returning to the same state restores the same internal energy. Work and heating depend on the path taken and need not be zero over the cycle.
10. A sealed flask of gas is carried on a train moving at a steady high speed. Which energy is NOT part of the internal energy of the gas?
A
The kinetic energy of the flask and gas moving with the train
B
The random kinetic energy of the molecules relative to the flask
C
The potential energy due to forces between the molecules
D
The rotational kinetic energy of the individual molecules
Show answer
Answer: A. Internal energy is the sum of the random kinetic and potential energies of the molecules. The ordered motion of the whole sample with the train is bulk kinetic energy, not internal energy.
48, each with the answer and a short explanation, across 2 topics: Internal energy, The first law of thermodynamics. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Physics (A2) chapter 5 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
