A substitution (exchange) reaction is a reaction in which an atom or ion in a compound is replaced by another atom or ion. Such reactions are common both in the chemistry of metals and acids and in organic chemistry. A single substitution involves one element replacing another, whereas a double substitution (metathesis) involves two compounds exchanging partners.

置换(交换)反应是化合物中的某原子或离子被另一原子或离子取代的反应。这类反应在金属与酸的化学以及有机化学中都很常见。单置换涉及一种元素取代另一种元素,而双置换(复分解)则涉及两种化合物交换组分。