Every chemical reaction involves an energy change. When you burn wood, dissolve salt, or bake a cake, energy is either released to the surroundings or absorbed from them. Chemical energetics is the study of these energy changes, and understanding them is essential for making sense of why reactions happen and how we can control them.

In this chapter, we explore the distinction between exothermic and endothermic reactions, and introduce enthalpy change as the chemist's way of measuring and expressing energy transfers. We then look at activation energy and reaction pathway diagrams, before examining the connection between bond breaking and bond making and the overall energy change of a reaction. By the end of the chapter, you will be able to calculate enthalpy changes using bond energies, a skill that brings together both conceptual understanding and quantitative reasoning.