What type of reaction occurs when one element in a compound is replaced by another element?

A single-replacement reaction, also known as a single displacement reaction, occurs when one element in a compound is replaced by another element. This type of reaction typically involves a more reactive element displacing a less reactive element from a compound. For example, if you take a solution of copper(II) sulfate and place a piece of zinc in it, the zinc will replace the copper in the compound, resulting in the formation of zinc sulfate and copper metal.

This reaction is characterized by the general form:

A + BC → AC + B,

where A is the replacing element, and BC is the compound from which the element is being replaced. The reaction is driven by the relative reactivity of the elements involved, following the activity series of metals, which ranks elements based on their ability to displace others from compounds.

Understanding the other types of reactions can help clarify why single-replacement is distinct. A double replacement reaction involves two compounds exchanging components, while a combination reaction sees two or more reactants forming a single product. Decomposition reactions involve a single compound breaking down into two or more simpler products. Each of these types has unique characteristics, but only the single-replacement reaction specifically involves one element in a compound being exchanged for another element.