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Leaving Cert Physics & Chemistry: Kinetic theory

How often Kinetic theory 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 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Kinetic theory, Higher Level(7 marks)

Quick ones on Kinetic theory.

(a)Which is an assumption of the kinetic theory of an ideal gas?
  1. Molecules attract each other strongly at all times
  2. Collisions between molecules are perfectly elastic
  3. Molecules stop moving completely when cooled to 0 °C
(b)What does the Brownian motion of smoke particles in a smoke cell show?
  1. Air is less dense than smoke
  2. Smoke particles are attracted by light
  3. Air molecules are in constant random motion
(c)According to kinetic theory, what causes the pressure of a gas?
  1. Molecules colliding with the container walls
  2. The weight of molecules pressing down
  3. Molecules repelling each other at a distance
Show the answers

(a) Collisions between molecules are perfectly elastic

(b) Air molecules are in constant random motion

(c) Molecules colliding with the container walls

Your turn: Higher Level questions on Kinetic theory.

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
2025Q1(g), Q1(h)
2024Q1(j), Q4
2023Q1(e)
2022Q4
2021Q4
2019Q1(g), Q3
2018Q1(j)
2017Q4
2016Q4

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

Ordinary Level

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

Every paper, year by year

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

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

More Kinetic theory questions

Kinetic theory, 2 marks

Brownian motion of smoke particles in air shows that?

  1. Smoke particles are alive and swim
  2. Air is heavier than the smoke particles
  3. Air molecules are moving randomly
Show the answer

Air molecules are moving randomly

Seen in a smoke cell under a microscope, the smoke specks jiggle about. Unseen, fast-moving air molecules are hitting them unevenly.

Kinetic theory, 2 marks

According to the kinetic theory, gas pressure is caused by?

  1. The weight of the container pressing on the gas
  2. Molecules colliding with the container walls
  3. Molecules attracting each other in the container
Show the answer

Molecules colliding with the container walls

Each collision gives the wall a tiny push. Billions of collisions every second add up to a steady force on each square metre, which is pressure.

Kinetic theory, 2 marks

When a gas is heated, its molecules?

  1. Move faster on average
  2. Get bigger on average
  3. Stop colliding with walls
Show the answer

Move faster on average

Temperature is linked to the average kinetic energy of the molecules. Hotter molecules move faster and hit the walls harder and more often.

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry