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Subjects · Leaving Cert Physics & Chemistry

Leaving Cert Physics & Chemistry: Gas laws

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

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 8 of the last 9 Ordinary Level papers, most recently in 2025. most years

Gas laws, Higher Level(7 marks)

Quick ones on Gas laws.

(a)Boyle's law: for a fixed mass of gas at constant temperature…
  1. V/T is constant
  2. pV is constant
  3. p/T is constant
(b)200 cm³ of gas at 100 kPa is compressed to 50 cm³ at constant temperature. New pressure?
  1. 250 kPa
  2. 25 kPa
  3. 400 kPa
(c)Using pV = nRT with R = 8.31 J K⁻¹ mol⁻¹, the volume must be in…
  1. m³
  2. Litres
  3. cm³
Show the answers

(a) pV is constant

(b) 400 kPa

(c) m³

Your turn: Higher Level questions on Gas laws.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q4
2024Q1(l), Q4
2023Q1(g), Q3
2022Q1(g), Q4
2021Q1(f), Q4
2019Q1(h), Q3
2018Q1(h), Q4
2017Q4
2016Q4

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

More Gas laws questions

Gas laws, 2 marks

The pressure law: at constant volume, the pressure of a fixed mass of gas is proportional to its…

  1. Celsius temperature
  2. Density
  3. Kelvin temperature
Show the answer

Kelvin temperature

p/T is constant only when T is in kelvin. With Celsius, the pressure would be zero at 0 °C, which is false.

Gas laws, 2 marks

One pascal is a pressure of…

  1. 1 J s⁻¹
  2. 1 N m⁻²
  3. 1 N m
Show the answer

1 N m⁻²

Pressure = force ÷ area, so 1 Pa = 1 newton per square metre. 1 N m is a unit of work (a joule); 1 J s⁻¹ is a watt.

Ordinary Level

Asked on 8 of the last 9 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025Q4
2024Q1(g), Q4
2023Q4
2022Q1(j)
2021Q1(e)
2019Q4
2018Not asked
2017Q4
2016Q4

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

More Gas laws questions

Gas laws, 2 marks

Boyle's law: at constant temperature, the pressure of a fixed mass of gas is?

  1. Directly proportional to its volume
  2. Independent of its volume
  3. Inversely proportional to its volume
Show the answer

Inversely proportional to its volume

pV = constant. Halve the volume and the pressure doubles. The temperature and the mass of gas must stay fixed.

Gas laws, 2 marks

Charles' law: at constant pressure, the volume of a fixed mass of gas is proportional to?

  1. Its pressure
  2. Its temperature in kelvin
  3. Its temperature in °C
Show the answer

Its temperature in kelvin

V ∝ T only when T is in kelvin. A V against θ (°C) graph is a straight line that meets the axis at about −273 °C, not at 0 °C.

Gas laws, 3 marks

A gas at 100 kPa fills 6 L. It is squeezed to 2 L at constant temperature. New pressure?

  1. 300 kPa
  2. 33.3 kPa
  3. 600 kPa
Show the answer

300 kPa

p1V1 = p2V2, so 100 × 6 = p2 × 2, giving p2 = 600 ÷ 2 = 300 kPa. Smaller volume means higher pressure.

Other Physics & Chemistry topics

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