1Hotter or colder?
Some reactions make their surroundings hotter. Others make them colder. A thermometer shows which.
temperature
Lesson 17.1 notes
Exothermic and endothermic
Reactions that give out energy and reactions that take it in, and how a thermometer tells you which.
2Exothermic: energy out
An exothermic reaction gives out energy to its surroundings, so the temperature goes up.
exothermic
3Endothermic: energy in
An endothermic reaction takes in energy from its surroundings, so the temperature goes down.
endothermic
4The surroundings
The surroundings are everything around the reaction: the water, the container and the air. As they gain energy, their particles move faster.
surroundings
5Exothermic all around
Burning, respiration, neutralisation and iron hand warmers all give out energy.
6Endothermic all around
Photosynthesis, thermal decomposition and the dissolving inside instant cold packs all take in energy.
7There is no “cold” coming out
A cold pack feels cold because energy flows out of your hand and into the pack. Nothing called “cold” comes out of it.
Explore: Reaction lab
Choose a reaction and watch the thermometer and the graph.
Common mistake: Endothermic reactions do not give out “cold”
An endothermic reaction feels cold because it takes energy in from its surroundings, including your hand. Nothing called “cold” flows out: energy flows in.
Remember
- Exothermic: energy is given out, so the surroundings get hotter.
- Endothermic: energy is taken in, so the surroundings get colder.
- Burning, respiration and neutralisation are exothermic. Photosynthesis and thermal decomposition are endothermic.
Going further at GCSE
GCSE: Exothermic and endothermic reactions → GCSE: Energy changes →