GCSE Physics (AQA)

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Cooling Graphs

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Particle model of matter Internal energy and energy transfers

Cooling Graphs

2:07 Heating to Change State
Spec 4.3.2.3
Previous Heating Graphs Next Kinetic Theory of a Gas
  • The rate at which an object cools changes with its temperature.
  • Temperature changes over time can be represented on a graph.
  • Initially, the temperature drops quickly, then slows down as heat flow to the surroundings decreases when temperatures become closer.
  • During exams, detailed understanding of this process is not required.
  • An object changes state if it passes its boiling or melting point when cooling.
  • Example: Hot tea and melted chocolate cooling to room temperature from around 40��C to 20��C.
  • Tea remains liquid as its temperature doesn't drop below its melting point (0��C).
  • Chocolate becomes solid as its temperature drops below its melting point (30��C).
  • During a change of state, the temperature remains constant for a period.
  • On a cooling graph, the gradient changes and there is a horizontal section indicating the freezing point.
  • No kinetic energy is lost during the horizontal section; bonds form instead.
  • The graph's gradient changes again after the change of state, similar to the initial cooling phase.
  • Heat flow to the surroundings slows as temperatures become closer.
  • Cooling graphs have smooth transitions between sections, unlike heating graphs.

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