Potential chemical energy is stored in materials and released through chemical reactions as heat or light. Strong bonds store less energy and require more energy to break, while weak bonds store more energy and require less energy to break. Fossil fuels contain large amounts of potential chemical energy, which is released through burning. Energy density is expressed in megajoules per kilogram and explosives release their energy quickly.
Potential chemical energy is energy stored in a material that can be released through a chemical reaction. This energy can come from the combination of atoms or molecules or from the breaking of molecules. It is released as heat, light, or both. Usually some type of trigger is needed to release potential energy, but this can be as simple as simply mixing two materials together, such as adding the highly reactive metal, potassium, with water, resulting in a very strong reaction that releases a lot of heat.
The making and breaking of bonds between atoms is the source of all potential chemical energy. Depending on the strength of those bonds, the amount of energy stored will vary. Very strong bonds store a small amount of energy and weak bonds store larger amounts. Strong bonds are very stable and require additional energy to break, meaning less energy is released when they are broken. The opposite is true for weak bonds, so they require little additional energy as a trigger to break and release a large amount of energy.
This principle of potential chemical energy underlies our use of many of the world’s energy sources. Hydrocarbon fuels, also known as fossil fuels, such as coal, petroleum and its refined derivatives contain very large amounts of potential chemical energy. When burned, the molecules of these substances are combined with oxygen. This results in the breaking of some of the molecular bonds between some atoms in the molecules and the formation of others as oxygen atoms become incorporated into the molecular structure, a process known as oxidation. The result is the release of potential chemical energy in the form of heat and light, but mostly heat, which is harnessed and used to power machines and converted into electricity.
Stored energy is expressed in international standard (SI) units of megajoules per kilogram (Mj/kg), and the amount of energy stored in a substance in relation to a given mass is called its energy density. This allows you to compare the amount of potential chemical energy stored in one substance versus another by mass. This type of energy can be released in several ways. For fossil fuels, it is usually released by burning. For substances such as food, it is released during the body’s metabolic processes, which are chemically identical to combustion, but are performed at a much slower and more controlled rate.
Explosives such as dynamite and nitroglycerin release their potential chemical energy very quickly, which gives them explosive properties. Most explosives have a relatively low amount of potential chemical energy by mass, even compared to things like sugar, but their chemical properties allow this energy to be released almost instantaneously. For example, nitroglycerin contains 6.5 Mj/kg and raw sugar cane contains 19 Mj/kg.
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