Quick answer: An ideal gas obeys pV = nRT, where pressure, volume and kelvin temperature are linked through the amount of gas. This Physics 11-12 test on ideal gas equation has 9 questions worth 20 marks, to do in 45 minutes: ideal gas assumptions, helium cylinder and heating fourfold. The mark scheme is on a separate page; free printable PDF.
This test covers the gas equation, kinetic theory, internal energy and thermal energy changes. Use R = 8.31 J/(mol K), k = 1.38 × 10⁻²³ J/K and NA = 6.02 × 10²³ mol⁻¹. Show every step of the working and give each result with its unit.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB B.1-B.3
Question 1 Ideal gas assumptions (2 marks)
State two assumptions of the kinetic model of an ideal gas.
Question 2 Helium cylinder (3 marks)
A 25 L cylinder contains helium at 4.0 × 10⁵ Pa and 17 °C.
- Calculate the amount of helium in the cylinder. (2 marks)
- Calculate the number of helium atoms. (1 mark)
Question 3 Heating fourfold (3 marks)
A fixed amount of ideal gas is heated from 300 K to 1200 K.
- State the factor by which the r.m.s. speed of the molecules increases. (1 mark)
- Calculate the mean kinetic energy of a molecule at 1200 K. (2 marks)
Question 4 Sealed can in a fire (2 marks)
Explain, using the kinetic model, why the pressure inside a sealed rigid can increases when the can is heated.
Question 5 Heating wax: melting (2 marks)
The graph shows the temperature of 0.50 kg of solid wax heated by a 400 W heater, with no energy lost.
- State the melting point of the wax. (1 mark)
- Explain why the temperature stays constant during melting. (1 mark)
Question 6 Heating wax: solid (2 marks)
Use the graph of the previous question to calculate the specific heat capacity of the solid wax.
Question 7 Heating wax: latent heat (2 marks)
From the flat section of the graph, determine the energy absorbed while the wax melts, and hence its specific latent heat of fusion.
Question 8 Kettle boiling dry (3 marks)
A 2.2 kW kettle keeps boiling after the thermostat has failed. The latent heat of vaporisation of water is 2.26 × 10⁶ J/kg.
- Calculate the energy supplied in 90 s. (1 mark)
- Calculate the mass of water turned into steam in that time. (2 marks)
Question 9 No potential energy (1 mark)
State why the internal energy of an ideal gas contains no intermolecular potential energy.
