Energy Changes

Energy Changes covers exothermic and endothermic reactions, energy level diagrams, activation energy, bond energy calculations and, for Triple students, cells, batteries and fuel cells.

The unit is small but precise. An exothermic reaction releases energy to the surroundings and the temperature rises; an endothermic reaction takes energy in and the temperature falls. Energy level diagrams must show the products lower than the reactants for an exothermic change, with the activation energy marked from the reactants to the peak. Bond energy calculations follow one method: energy in to break bonds, minus energy out from making them. A negative answer means exothermic. The most common errors are reversing that subtraction and forgetting to multiply by the number of each bond in the molecule.