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Leaving Cert Chemistry: Gas laws

How often Gas laws comes up on the Chemistry papers, every year it was asked, and questions to try.

HL Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

June 2027 is the first exam on the new Chemistry course. These come from the 2016–2026 papers, so read them as a guide.

Gas laws, Higher Level(6 marks)

Quick ones on Gas laws.

(a)Avogadro's law states that equal volumes of gases at the same temperature and pressure contain?
  1. Equal masses of gas
  2. Equal numbers of molecules
  3. Equal numbers of atoms
(b)Boyle's law states that, at constant temperature, the volume of a fixed mass of gas is?
  1. Directly proportional to the temperature
  2. Directly proportional to the pressure
  3. Inversely proportional to the pressure
(c)Combined gas law equation?
  1. p1V1 / T1 = p2V2 / T2
  2. p1T1 / V1 = p2T2 / V2
  3. p1V1 x T1 = p2V2 x T2
Show the answers

(a) Equal numbers of molecules

(b) Inversely proportional to the pressure

(c) p1V1 / T1 = p2V2 / T2

Your turn: Higher Level questions on Gas laws.

Higher Level

Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q10(b)
2025Q4(f)
2024Q4(c), Q4(d)
2023Q4(e), Q11(a)
2022Q4(e), Q10(a)
2021Q4(d), Q4(g)
2019Q3, Q4(c), Q10(c)
2018Q4(d)
2017Q4(e), Q10(a)
2016Q4(f), Q11(a)

Links open the State Examinations Commission’s paper for that year.

More Gas laws questions

Gas laws, 2 marks

Value of the gas constant R used in pV = nRT?

  1. 22.4 L per mol
  2. 6.022 x 10^23 per mol
  3. 8.314 J per K per mol
Show the answer

8.314 J per K per mol

Use SI units with it: p in Pa, V in m3, T in K. 22.4 L per mol is the molar volume at s.t.p. and 6.022 x 10^23 is the Avogadro constant.

Gas laws, 3 marks

Volume of 1.0 mol of an ideal gas at 300 K and 100 000 Pa? (R = 8.31)

  1. 2.49 m3
  2. 0.0249 m3
  3. 0.0025 m3
Show the answer

0.0249 m3

V = nRT / p = 1.0 x 8.31 x 300 / 100 000 = 0.0249 m3, which is 24.9 litres.

Gas laws, 2 marks

To use pV = nRT in SI units, a volume of 500 cm3 must be entered as?

  1. 5.0 x 10^-4 m3
  2. 5.0 x 10^-3 m3
  3. 0.5 m3
Show the answer

5.0 x 10^-4 m3

1 m3 = 1 000 000 cm3, so 500 cm3 = 500 / 1 000 000 = 5.0 x 10^-4 m3.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q9
2025Q4(d), Q4(k), Q10(b)
2024Q4(i), Q11(b)
2023Q4(d)
2022Q10(c), Q11(b)
2021Q4(e), Q4(f), Q10(c)
2019Q4(b)
2018Q10(c), Q11(a)
2017Q4(e), Q4(h), Q10(c)
2016Q4(c), Q4(f)

Links open the State Examinations Commission’s paper for that year.

More Gas laws questions

Gas laws, 2 marks

Temperature in degrees Celsius equal to 0 K?

  1. 0
  2. 273
  3. -273
Show the answer

-273

0 K is absolute zero, the lowest possible temperature. Kelvin = Celsius + 273, so Celsius = 0 - 273 = -273.

Gas laws, 3 marks

2H2 + O2 gives 2H2O (all gases). Volume of oxygen needed to react with 100 cm3 of hydrogen?

  1. 200 cm3
  2. 50 cm3
  3. 100 cm3
Show the answer

50 cm3

Gay-Lussac's law: gases react in simple volume ratios. H2 to O2 is 2 to 1, so 100 cm3 of H2 needs 50 cm3 of O2.

Gas laws, 2 marks

At constant temperature, the pressure on a fixed mass of gas is doubled. Its volume?

  1. Halves
  2. Doubles
  3. Stays the same
Show the answer

Halves

Boyle's law: pressure times volume stays constant, so doubling the pressure halves the volume.

Other Chemistry topics

All of Leaving Cert Chemistry