Oxidation describes a common natural process where a substance combines with oxygen or, more broadly, loses electrons. This fundamental reaction occurs all around us, influencing many everyday phenomena. Understanding oxidation requires recognizing how matter transforms, either by changing its physical appearance or by fundamentally altering its chemical makeup.
Understanding Chemical and Physical Changes
Matter can undergo two main types of transformations: physical changes and chemical changes. A physical change alters a substance’s form or appearance but does not create new substances. For instance, melting an ice cube into water changes its state from solid to liquid, but the water molecules (H₂O) remain the same. These changes are often reversible.
Conversely, a chemical change results in the formation of entirely new substances with different properties from the originals. This type of transformation involves the breaking of existing chemical bonds and the formation of new ones. Burning wood, for example, transforms it into ash, smoke, and gases, none of which are wood. Chemical changes are typically difficult to reverse, and they often involve observable signs like a change in color, the production of heat or light, or the formation of a gas or precipitate.
Oxidation as a Chemical Change
Oxidation is a chemical change because it fundamentally alters the chemical composition of the substances involved. When a substance undergoes oxidation, its atoms rearrange to form new chemical compounds with distinct properties. This process involves the loss of electrons by one substance, which is then gained by another substance in a simultaneous reduction reaction. The transfer of electrons leads to the formation of new chemical bonds and the creation of different molecules.
Consider the rusting of iron, a classic example of oxidation. Iron metal, a silvery-gray solid, reacts with oxygen in the presence of water to form iron oxide, commonly known as rust. Rust is a reddish-brown, brittle substance with properties entirely different from pure iron. This transformation represents a change in chemical identity, as the iron atoms have bonded with oxygen atoms to create a new compound. The formation of this new substance confirms that rusting is not merely a change in appearance but a complete chemical transformation.
Everyday Examples of Oxidation
Oxidation is responsible for many familiar changes observed in daily life.
Another common instance is the browning of cut fruits, such as apples or avocados, when exposed to air. Enzymes within the fruit react with oxygen, leading to the formation of new pigments that cause the discoloration. This change in color indicates a chemical reaction has occurred. Similarly, the tarnishing of silver jewelry involves oxidation, where silver reacts with sulfur compounds in the air to form silver sulfide, a blackish substance.
Combustion, or burning, is also a rapid form of oxidation. When wood burns, it reacts vigorously with oxygen, producing ash, carbon dioxide, and water vapor. These products are entirely new substances with different chemical properties than the original wood. The release of heat and light during combustion further signifies the chemical transformation taking place.