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AQA GCSE · Question 01.2 · Particle Model of matter
Figure 2 shows how the temperature of the water varied with time.
What is the name of the process that is taking place between points A and B?
Give a reason for your answer.
Figure 2 shows how the temperature of the water varied with time.
What is the name of the process that is taking place between points A and B?
Give a reason for your answer.
How to approach this question
1. Identify the process: Look at the graph between A and B. The line is horizontal. What does this mean for the temperature? When a substance is heated and its temperature stops rising, what is happening?
2. Give the reason: Explain your answer from step 1 by referring to the graph. Describe what is happening to the temperature in the section A-B.
Full Answer
Process: Boiling (or vaporisation/evaporation)
Reason: The temperature is constant (even though heat is being supplied).
The graph shows that as time increases, the temperature initially rises. This is the water heating up. Between points A and B, time continues to pass (meaning energy is still being supplied), but the temperature remains constant. This flat section on a heating curve indicates a change of state. Since the water was being heated, this change of state is from liquid to gas, which is called boiling or vaporisation. The energy being supplied is used to break the bonds between water molecules (latent heat of vaporisation) rather than increasing their kinetic energy (temperature).
Common mistakes
✗ Stating "melting" - this happens from solid to liquid.
✗ Stating "condensing" - this is the reverse process, gas to liquid, and involves cooling.
✗ Giving a reason like "it is being heated" - this is true for the whole graph, not specific to the A-B section. The key reason is the constant temperature.
Practice the full AQA GCSE Physics Foundation Tier Paper 1
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