Exothermic and endothermic reactions, pathway diagrams
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Hot pack, cold pack
- Exothermic reactions
- Endothermic reactions
- Examples to learn
Read the transcript of the teaching part
Last time
Before we start: last time, in Bond energy calculations, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Hot pack, cold pack
A hand warmer gets hot when you crack it. A sports cold pack gets freezing when you squeeze it. Both are just chemical reactions. The difference is which way the energy goes, and a diagram can show it.
Exothermic reactions
In an exothermic reaction, energy is transferred to the surroundings, usually as heat. So the temperature of the surroundings goes up. The reaction mixture feels hot. The key word is exit. Exothermic: the energy exits.
Endothermic reactions
In an endothermic reaction, energy is taken in from the surroundings. So the temperature of the surroundings goes down. The mixture feels cold. Think of it as entering. Endothermic: the energy enters.
Examples to learn
Exothermic: burning fuels, neutralisation, respiration, and adding water to calcium oxide. Endothermic: thermal decomposition, such as heating calcium carbonate, and photosynthesis. Dissolving ammonium nitrate or ammonium chloride in water is endothermic too, so the water gets cold.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Exothermic and endothermic reactions · Reaction pathway diagrams · Exothermic and endothermic reactions · Reaction pathway diagrams.
The whole chapter: Chemical Energetics, Chemical Energetics.
Chapter 5: Chemical energetics
- Exothermic and endothermic reactions, pathway diagrams 6 min
- Bond energy calculations 8 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.