The questions are on the kinetic theory of gases test. Take it under real conditions before reading the mark scheme.
Quick answer: Gas pressure is caused by particles colliding with the walls of their container. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on kinetic theory of gases, from temperature scale to condition for Boyle’s law, with the equivalent answers to accept.
This is the kinetic theory of gases test answers for physics grades 9-10, with the marks for each answer. First sit the test without notes, then mark it here and revise with the lesson.
Award each mark as shown. Accept any equivalent correct wording. Allow follow-through from a wrong earlier answer, and do not penalise sensible rounding to 2 or 3 significant figures. A missing unit costs at most one mark in the whole paper.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: IGCSE 2.1, HS-PS3-2
Kinetic theory of gases test answers: answers and marks
Question 1 Temperature scale (2 marks)
- −273 °C.
- 37 + 273 = 310 K.
Marking: 1 mark each part.
Question 2 How gas creates pressure (3 marks)
The particles move randomly at high speed. They collide with the walls and bounce back, which changes their momentum and so exerts a force. Very many collisions each second give a steady force on each unit of area, which is the pressure.Marking: random motion / collisions with walls (1); each collision gives a force (1); many collisions give steady pressure = force per area (1).
Question 3 Pump (3 marks)
p2 = p1V1 / V2 = 100 × 250 / 40 = 625 kPa.Marking: law used (1), substitution (1), answer with unit (1).
Question 4 Syringe and gauge (4 marks)
- 150 × 30 = 4500 kPa cm³.
- p = 4500 / 18 = 250 kPa.
- The temperature (and the mass of gas).
Marking: (a) 1; (b) rearrangement 1, answer 1; (c) 1.
Question 5 Heating a cylinder (3 marks)
T1 = 288 K and T2 = 348 K. p2 = 200 × 348 / 288 = 241.7 = 242 kPa.Marking: conversion to kelvin (1), substitution (1), answer (1).
Question 6 Pressure rise on heating (2 marks)
The particles gain kinetic energy and move faster, so they hit the walls harder. They also hit the walls more often because they travel faster across a fixed volume, so the force per unit area increases.Marking: faster particles (1); harder and more frequent collisions (1).
Question 7 Lowest temperature (2 marks)
At −273 °C (0 K) the particles have the lowest possible kinetic energy, so their motion cannot slow down any further. There is no lower energy state, so no lower temperature exists.Marking: particles have minimum energy (1); cannot lose any more (1).
Question 8 Condition for Boyle’s law (1 mark)
Constant temperature (or a fixed mass of gas).Marking: 1 mark for either condition.
