Three and four mark questions
These are similar to one- and two-mark questions but you will be expected to write in more depth for three- and four-mark questions.
The answers here give lists of valid points that could be included in your answer.
This page contains AQA material which is reproduced by permission of AQA.
Sample question 1 - Foundation
Question
Explain why heating a gas increases the average speed of the gas particles. [3 marks]
Heating a gas increases its temperature [1]. The temperature is proportional to kinetic energy [1]. If the kinetic energy of a gas increases then the speed of the gas particles increases [1].
Answers should include scientific key words. It may be helpful to plan which key words are going to be used and use these to help structure the answer, eg temperature, kinetic energy, speed.
Sample question 2 - Higher
Question
When the gas in a container with a fixed volume is heated, the pressure increases as the temperature increases.
Explain why the pressure increases. [4 marks]
Increasing the temperature also increases the kinetic energy of the gas particles [1]. The speed of the particles increases with kinetic energy [1]. Because the particles are moving faster they collide more frequently with the walls of the container [1]. This means that a greater force is applied to the walls of the container and so the pressure increases [1].
Answers should include scientific key words. It may be helpful to plan which key words are going to be used and use these to help structure the answer, eg temperature, kinetic energy, speed, collisions, force.
Sample question 3 - Higher
Question
Central heating boilers burn gas and use the energy released to heat water. Modern condensing central heating boilers take advantage of the energy that is released when water condenses.
Waste water vapour produced when the water is heated in the boiler is used to preheat the cold water entering the boiler.
Give some of the arguments in favour of condensing boilers compared to older non-condensing boilers. [4 marks]
Preheating the water means less energy is needed to heat the water, and as less energy is wasted, the condensing boilers are more efficient. Less gas is burned to heat the same amount of water, meaning they are cheaper to run and less CO2 is produced.
Answers may include any four points from:
- because the water is preheated, the change in temperature of the water is less
- so less energy is used to heat the water (E=mc∆θ)
- therefore condensing boilers are more efficient
- so less energy is wasted
- less gas is burned to heat the same amount of water
- less waste gas (CO2) is produced by the boiler or (because less gas is used) they are cheaper to run/save money
[4]
