Exothermic and endothermic reactions

The idea

Energy is conserved in reactions. An exothermic reaction transfers energy to the surroundings, so their temperature rises: combustion, oxidation and neutralisation. An endothermic reaction takes in energy, so the temperature falls: thermal decomposition and the reaction of citric acid with sodium hydrogencarbonate. Reaction profiles show the relative energies of reactants and products, and the activation energy: the minimum energy particles need to react.

1. Measure the temperature change.
2. Rise means exothermic; fall means endothermic.
3. On a profile, compare the energy of reactants and products.

Watch out In an exothermic profile the products are lower in energy than the reactants.