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O-Level Kinetic Particle Model of Matter

What the O-Level syllabus expects for Kinetic Particle Model of Matter, and how to practise it.

What the syllabus expects

Contrast how physical properties differ across solids, liquids and gases.
Apply the kinetic particle model to describe solids, liquids and gases, linking their properties to how the particles (such as molecules and atoms) are arranged and move and to the forces and separations between them.
Deduce from a Brownian motion experiment the evidence it gives for the random motion of molecules in a liquid or gas.
Connect a body's temperature rise to the increase in the average kinetic energy of all its particles.
Account for a gas's pressure in terms of how its particles move.

How it's examined

Questions on this topic most often ask you to describe, explain. About 4% of the past-paper style questions in Rae's bank for this subject sit in this topic.

Worked examples

Example 1 (2 marks)

(b) Using ideas about the gas particles, explain how the gas produces a pressure on the inner walls of the syringe.

Show the worked answer

The gas particles are in continuous rapid random motion. They repeatedly collide with the inner walls of the syringe. At each collision a particle's momentum changes, so the wall exerts a force on the particle and, by Newton's third law, the particle exerts an equal and opposite force on the wall. The huge number of such collisions per second, spread over the wall area, produces a steady average force per unit area, which is the pressure on the walls.

Example 2 (2 marks)

(d) Describe what happens to the pressure a gas exerts when its volume is halved while the temperature stays fixed. Justify your answer.