.1 Energy transfer during exo and endothermic reactions

• Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place. If a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants, by the amount transferred.
• An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases.
• Exothermic reactions include combustion, many oxidation reactions and neutralisation.
• Everyday uses of exothermic reactions include self-heating cans and hand warmers
• An endothermic reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases
• Endothermic reactions include thermal decompositions and the reaction of citric acid and sodium hydrogencarbonate. Some sports injury packs are based on endothermic reactions.