Chemical reactions involve changes in energy as bonds between atoms are broken or formed. Some reactions release energy into their surroundings, often as heat or light, while others absorb energy to proceed. This energy handling defines a reaction as either exothermic or endothermic.
Understanding Exothermic and Endothermic Reactions
Exothermic reactions release energy into their environment, often as heat, causing the surroundings to become warmer. Burning wood is a common example, where stored chemical energy converts into heat and light.
Conversely, endothermic reactions absorb energy from their surroundings. This absorption causes the temperature of the surroundings to drop, making them feel colder. Instant cold packs, which become noticeably cool when activated, illustrate an endothermic process.
Why Most Oxidation Releases Energy
Oxidation is a chemical reaction that generally involves the loss of electrons from a substance or its combination with oxygen. Most oxidation reactions are typically exothermic, meaning they release energy. This energy release occurs because the formation of new chemical bonds during oxidation often results in products that are more stable and have lower energy than the initial reactants. This increased stability of the products drives the overall energy release.
When new, stronger chemical bonds form, energy is released. If the energy released from forming these bonds, such as those with oxygen, is greater than the energy required to break original bonds in the reactants, there is a net release of energy. While oxidation broadly encompasses electron loss, and some specific steps might require energy input, most familiar oxidation reactions are characterized by this energy release.
Everyday Examples of Oxidation
Everyday phenomena demonstrate exothermic oxidation, ranging from rapid reactions to slow, subtle processes.
Combustion, or burning, is a prime example of rapid oxidation. Substances like wood in a campfire, natural gas in a stove, or wax in a candle combine with oxygen, releasing substantial heat and light.
Rusting, or corrosion, is a slower form of oxidation where iron reacts with oxygen and water to form iron oxides. This process also releases energy, but it occurs so gradually that the heat generated is not easily perceptible.
Cellular respiration is a biological oxidation process that occurs within living organisms. Our bodies “burn” glucose from food using oxygen to generate energy for various life functions, primarily as adenosine triphosphate (ATP). This controlled oxidation ensures a continuous energy supply for all cellular activities.