In Module 1, you were introduced to measurements, the process of science and a little about energy. In Module 2, you learned about the atom. Through breaking apart nuclei (fission) or fusing together small nuclei (fusion), great amounts of energy can be released. However, much of what we do in chemistry does not rely only on the nuclei of atoms. In Module 3, you will learn about how atoms are combined to form molecules. By breaking apart and forming certain molecules, energy can be released. For example, in the car engines, a combustion reaction takes place between gasoline and oxygen to produce water and carbon dioxide and energy! By understanding how molecules are formed and that these molecules undergo chemical reactions, you will gain a better idea about energy production. Combustion reactions are not the only reactions that release energy. Many chemical reactions produce energy, but there is a need to look at other processes that produce energy (like wind, solar and geothermal) to help when our reactants (fuels) run low and to reduce the environmental impact of the combustion of fossil fuels. Figure 1: How much energy does the world consume? (Source: Our World is Data , CC BY 4.0)