Types of Chemical Reactions

A chemical reaction occurs when the atoms of a substance are recombined to make something new. After mixing ingredients together, you can tell a chemical change has happened if you observe any of the following:

• Bubbles are given off
• A change in temperature occurs
• Light is emitted
• A solid precipitate forms
• An odor is detected

This article describes the six main types of chemical reactions that can produce these results.

Combustion

Combustion occurs when a hydrocarbon such as propane or gasoline burns. The products of combustion are water, carbon dioxide, and energy, although incomplete combustion can also produce soot and carbon monoxide. An everyday example of a combustion reaction is when a fuel injection engine combines diesel fuel with oxygen to create energy.

Synthesis

When two different substances are combined to make something new, chemists refer to the process as a synthesis reaction. For example, when explosive sodium metal is combined with deadly chlorine gas, the resulting product is edible table salt, sodium chloride.

Decomposition

Decomposition can occur slowly or quickly. For example, household hydrogen peroxide is sold in brown bottles because, over time, sunlight will turn it into water and oxygen gas. This decomposition reaction can be sped up considerably by the addition of yeast, which acts as a catalyst.

Single Replacement

In single replacement reactions, one atom in a compound is traded for a different atom. If you cover a rusty ball bearing with aluminum foil and strike it against another one, aluminum atoms will replace the iron atoms in the rust. Sparks of heat reaching thousands of degrees also will be emitted in the process, so watch out!

Double Replacement

Double replacement reactions are similar to a single replacement, except that instead of just one atom in a substance being replaced, both atoms are swapped. For example, when lead nitrate is mixed with potassium iodide, lead combines with iodine to make beautiful, albeit poisonous, golden crystals.

Oxidation-Reduction

The sixth kind of reaction is oxidation-reduction, commonly referred to as redox. In redox reactions, one substance gives up some of its electrons to another substance. The name comes from the terms reduction, which means gaining electrons, and oxidation, which means losing electrons. A familiar example is the rusting of metals, in which case the metal gives up its electrons to oxygen in the air or in water.

Chemical reactions are part of our everyday lives. How many different types will you observe today?