chemistry laboratory

All About Chemical Reactions: From Oxidation and Reduction to Combustion and More!

Updated by Jim Deckebach

Studying chemistry is one of the best ways to make sense of the world around you. Chemistry is the study of how different forms of matter interact with each other. The interaction between these different materials is called a chemical reaction.

A chemical reaction is a process that creates an end result (the product) different from the materials we started with (the reactants). In other words, two or more things combine to become something else. If that basic concept sounds simple, that's because it is. However, the idea expands considerably when we consider all of the possible types of chemical reactions.

The Four Basic Reaction Types

The four basic types of chemical reactions are synthesis, decomposition, single replacement, and double replacement.


Synthesis is the combination of two or more simple substances, and the result is a more complex product. Carbon dioxide, the most abundant chemical compound in Earth's atmosphere, is formed by the synthesis of carbon and oxygen. A subset of synthesis reactions called organic synthesis deals with the intentional creation of new organic compounds.


Decomposition is the opposite of synthesis. In decomposition, a complex substance breaks down into its component parts. For example, the process of electrolysis breaks down water into hydrogen and oxygen. This process is reversible, as the hydrogen and oxygen can often be recombined into water by means of synthesis. Fermentation, the process that produces wine and beer, is also a type of decomposition reaction.

Single Replacement

Single replacement refers to the process of one element trading places with another in a compound. The elements that exchange places can be anions (negatively charged ions) or cations (positively charged ions).

Double Replacement

A double replacement reaction goes a step further. In this type of reaction, both anions and cations trade places. This type of reaction can be observed by introducing silver nitrate and sodium chloride to a water solution. When the reactants dissolve in the water, their ions combine to form entirely new products: silver chloride and sodium nitrate.


Combustion is a chemical reaction in which one or more elements interact with oxygen, producing heat, light, or both. We're familiar with combustion in everyday life: Even the simple act of lighting a match is an example of a combustion reaction. Striking a match causes friction to heat the head of the match, releasing chemicals into the air. The chemicals react with oxygen to create a flame.

Oxidation and Reduction

Reduction-oxidation (or "redox") reactions occur when electrons are transferred from one material to another. Oxidation is the process of a molecule, atom, or ion losing an electron. The flip side of this equation is reduction, in which a molecule, atom, or ion gains an electron. We can readily observe oxidation when we see iron oxide, or rust, form on metal.


In complexation reactions, individual molecules, ions, or atoms combine to create a large ion or molecule. The result is known as a coordination complex. One common use of complexation is in pharmaceutical medicine. Because some drugs are not highly water-soluble, it is sometimes necessary to bind these medicines to other elements. Doing so increases solubility and bioavailability, or the human body's ability to absorb them.

Acid-Base Reactions

In an acid-base reaction, protons transfer from one material to another. The substance losing the proton is the acid, and the substance that gains the proton is called the base. One common example of an acid-base reaction is found in food preparation: Acids can be used to marinate meats, such as when adding lemon to a piece of fish.


Precipitation is the formation of a solid. The new solid might form in a solution or within another solid. A common use for precipitation reactions is in wastewater treatment. Reagents are added to dissolved substances, forming an insoluble compound. This allows harmful chemicals to be precipitated out of the water.

Solid-State Reactions

Solid-state reactions occur, as the name indicates, between two solids. Solid-state reactions tend to be slow, at least in comparison to liquid and gas reactions. In some cases, such as thermal energy storage, this is an advantage. Solid-state reactions can be more reliable in a variety of temperature ranges than gas or liquid reactions would be.

Reactions at the Solid/Gas Interface

The surface between a solid and a gas is referred to as the solid/gas interface. When a reaction occurs at this boundary, it is called a solid/gas interface reaction. This type of reaction, sometimes called catalysis, is difficult to observe and study. Catalysis reactions are more prevalent in ultra-high vacuum environments and usually require scanning tunneling microscopes to observe.

Photochemical Reactions

Any chemical reaction in which atoms and molecules absorb photons and increase their energy is called a photochemical reaction. The most common reaction of this type in daily life is photosynthesis, the process by which plants turn sunlight into food. Photosensitive plants use the energy from sunlight to convert carbon dioxide and water into glucose. Similarly, humans convert ultraviolet radiation from the sun into vitamin D.


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