Ideal gases: past paper questions
Real questions on ideal gases
The newest 20 of 123 written questions, plus 2 multiple-choice. Open one to see it on the real paper.
- 9702/41 · October/November 2025 · Q4b(i)[1]
State what is indicated about the nature of the gas from the variation shown in Fig. 4.1.
See it on the paper → - 9702/41 · October/November 2025 · Q4b(ii)[2]
Determine the number N of molecules of the gas in the sample. N =
See it on the paper → - 9702/41 · October/November 2025 · Q4b(iii)[1]
Use your answer in (b)(ii) to determine the amount n of gas in the sample. n = mol
See it on the paper → - 9702/41 · October/November 2025 · Q4c[4]
The root-mean-square (r.m.s.) speed of the molecules of the gas is 1900 m s –1 when pV is equal to 270 J. Determine the mass, in u, of one molecule of the gas, where u is the unified atomic mass unit. mass = u
See it on the paper → - 9702/41 · October/November 2025 · Q8b(i)[3]
Calculate the mass, in u, of the uranium-238 nuclide. Give your answer to five decimal places. mass = u
See it on the paper → - 9702/42 · October/November 2025 · Q2b[2]
State two other basic assumptions of the kinetic theory of gases. (b) One of the basic assumptions of the kinetic theory of gases is that there are no forces exerted between the molecules of the gas except during collisions.
See it on the paper → - 9702/42 · October/November 2025 · Q2c(i)[2]
Determine the pressure of the gas. pressure = Pa
See it on the paper → - 9702/42 · October/November 2025 · Q2c(ii)[2]
Estimate the average separation of the hydrogen molecules in the gas. average separation = m
See it on the paper → - 9702/43 · October/November 2025 · Q4b(i)[1]
State what is indicated about the nature of the gas from the variation shown in Fig. 4.1.
See it on the paper → - 9702/43 · October/November 2025 · Q4b(ii)[2]
Determine the number N of molecules of the gas in the sample. N =
See it on the paper → - 9702/43 · October/November 2025 · Q4b(iii)[1]
Use your answer in (b)(ii) to determine the amount n of gas in the sample. n = mol
See it on the paper → - 9702/43 · October/November 2025 · Q4c[4]
The root-mean-square (r.m.s.) speed of the molecules of the gas is 1900 m s –1 when pV is equal to 270 J. Determine the mass, in u, of one molecule of the gas, where u is the unified atomic mass unit. mass = u
See it on the paper → - 9702/43 · October/November 2025 · Q8b(i)[3]
Calculate the mass, in u, of the uranium-238 nuclide. Give your answer to five decimal places. mass = u
See it on the paper → - 9702/42 · February/March 2025 · Q3b(iii)[2]
The mass of a nitrogen molecule is 4.7 × 10 –26 kg. Calculate the root‑mean‑square (r.m.s.) speed of a nitrogen molecule at 210 °C. r.m.s. speed = m s –1
See it on the paper → - 9702/41 · October/November 2024 · Q3b(i)[4]
Complete Table 3.1 by giving expressions, in terms of some or all of N, m, T, V and the constants in (a)(ii), for the quantities indicated. Table 3.1 sample X sample Y pressure internal energy mean-square speed of molecules amount of substance
See it on the paper → - 9702/41 · October/November 2024 · Q3b(ii)[2]
The temperature of sample X is now varied. On Fig. 3.1, sketch the variation with thermodynamic temperature of the root-mean- square (r.m.s.) speed of the molecules of the gas. r.m.s. speed 0 0 thermodynamic temperature Fig. 3.1
See it on the paper → - 9702/42 · October/November 2024 · Q4a[3]
State three of the basic assumptions of the kinetic theory of gases.
See it on the paper → - 9702/42 · October/November 2024 · Q4b[3]
Explain how molecular movement causes the pressure exerted by a gas.
See it on the paper → - 9702/42 · October/November 2024 · Q4c[3]
Fig. 4.1 shows the variation with thermodynamic temperature T of the mean‑square speeds 〈c 2 〉 for two gases X and Y. 6 〈c 2 〉 / 10 6 m 2 s –2 X 0 0 100 200 300 400 T / K Fig. 4.1 Y 2 4 Fig. 4.2 shows the variation with T of the product pV for samples of the two gases, where p is the pressure of the gas and V is th...
See it on the paper → - 9702/43 · October/November 2024 · Q3b(i)[4]
Complete Table 3.1 by giving expressions, in terms of some or all of N, m, T, V and the constants in (a)(ii), for the quantities indicated. Table 3.1 sample X sample Y pressure internal energy mean-square speed of molecules amount of substance
See it on the paper →
What examiners said
Generally well-answered by the stronger candidates. The common confusion among weaker candidates was the difference between r.m.s. speed and mean-square speed. Many candidates stopped at the mean-square speed and gave this as their answer to the r.m.s. speed.
— Examiner report, February/March 2025, 9702/42 Q3(b)(iii) (Cambridge)
Many of the more able candidates calculated the correct answer with relative ease, although a significant minority forgot to take the square root of their value of mean-square speed at the end. Some of the weaker candidates realised that the starting point required the mean kinetic energy to be equated with (3/2)kT, but then found the subsequent arithmetic difficult. Many others were a little conf...
— Examiner report, October/November 2023, 9702/42 Q2(d) (Cambridge)
Many candidates knew the meaning of the symbols. Candidates needed to make it clear that m is the mass of a single molecule. The wording used to describe the meaning of <c2> was sometimes unclear or incorrect. For example, ‘the mean square speed of the gas’ is not correct (as it relates to the molecules of the gas).
— Examiner report, October/November 2023, 9702/43 Q3(a)(i) (Cambridge)
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