Energy is the thread that runs through every reaction. Breaking the bonds in the reactants takes in energy, and making the bonds in the products gives out energy; whichever of the two is bigger decides whether the reaction warms its surroundings or cools them. That contrast is the difference between a hand warmer and an instant cold pack.
The first part of C5 is for everyone: exothermic and endothermic reactions, how to measure a temperature change, and how to read a reaction profile. The rest is Triple Chemistry only, looking at how chemical cells, batteries and fuel cells get a reaction’s energy out as electricity rather than heat.
🧭 How this topic splits by tier
Not all of C5 is for everyone. Check what your tier needs:
- Everyone: exothermic and endothermic reactions and their everyday uses, the required practical on temperature changes, and reaction profiles and activation energy.
- Higher Tier H: calculating the overall energy change of a reaction from bond energies.
- Triple (Chemistry only) T: chemical cells and batteries, and hydrogen fuel cells. (The electrode half equations within these are Higher Tier.)