Chemical energy is stored within the bonds of chemical compounds. This energy becomes available when these chemical bonds break or rearrange during a chemical reaction. It is a pervasive form of energy, present in various aspects of our surroundings, from the food that fuels our bodies to the fuels that power our vehicles. Understanding how chemical energy is stored and released helps to explain many processes in the natural world and in human technology.
Biological Energy Sources
Living organisms obtain chemical energy primarily from the food they consume, which contains energy-rich molecules like carbohydrates, fats, and proteins. These complex molecules are broken down through metabolic processes, releasing the stored energy. Inside cells, this energy is captured in the form of adenosine triphosphate (ATP), often called the energy currency of the cell. ATP stores energy in its phosphate bonds, and when one of these bonds is broken, energy is released to power cellular activities such as muscle contraction, nerve impulse transmission, and molecule synthesis. Plants, conversely, generate their own chemical energy through photosynthesis. This process converts light energy into chemical energy, storing it in glucose molecules, which are then used for growth.
Fossil Fuels and Their Derivatives
Chemical energy is also extensively stored in fossil fuels, which include coal, oil, and natural gas. These fuels formed over millions of years from the buried remains of ancient organic matter. The immense pressure and heat transformed this organic material into hydrocarbon compounds. When these fossil fuels are combusted, their chemical bonds break, releasing significant amounts of energy as heat and light. This process generates electricity in power plants, where heat boils water to produce steam that drives turbines. Derivatives like gasoline and diesel, refined from crude oil, power internal combustion engines in vehicles, converting their stored chemical energy into mechanical motion.
Batteries and Portable Power
Batteries store chemical energy and convert it into electrical energy through electrochemical reactions. In a typical battery, two different materials (electrodes) are separated by an electrolyte, which allows ions to move between them. When a circuit is completed, chemical reactions occur at the electrodes, causing electrons to flow and generate an electric current. Rechargeable batteries, like those in smartphones and electric vehicles, allow these chemical reactions to be reversed by applying an external electrical current, thereby restoring their stored chemical energy. Non-rechargeable batteries, such as common alkaline batteries, undergo irreversible chemical changes once their stored energy is depleted.
Everyday Chemical Reactions
Beyond biological systems, fossil fuels, and batteries, chemical energy is evident in other everyday reactions. The burning of wood in a fireplace, for instance, releases stored chemical energy as heat and light through combustion. Fireworks display a rapid release of chemical energy, producing light, sound, and heat. Processes like the slow rusting of iron, an oxidation reaction, and the chemical reactions in cleaning products that break down dirt and grime, also involve chemical energy transformations. Each chemical bond holds potential energy that can be released during reactions.