Metathesis is a bio-molecular process involving an exchange of bonds between two reacting chemical species, and results in the creation of new products with similar or identical bonding affiliations. For example, if you had chemical species AB and CD, they may react to give AD and CB.

The reaction, when written in the form of a chemical equation, would be expressed as seen below.

AB + CD → AD + CB

These chemical species can be either ionic or covalent. Precipitation reactions between solutions of ions in inorganic chemistry were formerly referred to as double displacement or double replacement reactions.

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