Chemical changes occur around us, and inside us, all the time. When chemical reactions happen, one or more new substances are formed and energy is either given off or absorbed in the process. Spontaneous chemical reactions, those that occur naturally under favourable conditions release free energy, meaning they are exergonic. Endergonic reactions, by contrast, require net energy input to make the reaction happen. This excellent learning resource explores energy associated with chemical reactions, and cover areas such as activation energy and product formation, standard heats of reaction, thermochemical equations and Hess' Law, and specific heat capacity and calorimetry. It is essential viewing for any chemistry student, providing clear explanations and easily understood visuals, including comprehensive chemical equations, about concepts that many students find challenging.