7.11 - Endothermic changes and reactions
Learn why an endothermic change takes in heat energy while its surroundings can become cooler. Use temperature evidence to distinguish this from an exothermic change.
Heat energy enters the change
Endothermic change or reaction
An endothermic change or reaction takes in heat energy from its surroundings.
For this energy-transfer model, treat the chemical change as the system. The water, container and air supply heat to it and are treated as the surroundings. Taking energy from the surroundings can lower their temperature. Cold is not a substance produced by the reaction; energy is transferred and conserved.
[DIAGRAM: asset_name: heat_energy_taken_in: Heat energy transfer in an endothermic change - diagram 1; asset_slug: 173_7_11_an_endothermic_change_or_reaction_as_one_in_which_heat_energy_is_taken_in_diagram1; file: diagram_assets/173_7_11_an_endothermic_change_or_reaction_as_one_in_which_heat_energy_is_taken_in_diagram1.png; recommended_method: deterministic_drawn; description: Monochrome deterministic diagram for Edexcel GCSE Chemistry 1CH0 7.11. It shows a beaker labelled system/change or reaction inside a dashed surroundings box labelled solution, cup, air and thermometer. Curved lines connect the surroundings and system; labels state that heat energy is taken into the system. Before and after thermometers show 22.0 degrees C falling to 17.5 degrees C, with labels explaining that the surroundings lose heat energy and the thermometer reading falls. Deterministic drawing is used because direction of heat transfer, labels and temperature-change interpretation are assessed content.]
The labels show heat entering the change and a thermometer reading falling from 22.0 °C to 17.5 °C. The curved lines illustrate the connection between the surroundings and the change; the written labels give the direction of transfer.
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