singledisplacement

Single-displacement, or single-replacement, is a type of chemical reaction in which an element reacts with a compound and displaces another element from that compound to form a new element and a new compound. The general form is A + BC → B + AC, where A replaces B.

It is a redox process: A is typically more reactive than B, so A is oxidized and B is reduced, yielding AC and freeing B. The driving force is the relative reactivity or standard reduction potentials. The reaction often occurs in aqueous solution or molten salts.

Reactions occur only when the entering element A is more reactive than the element it replaces. Predictability uses activity series for metals or standard reduction potentials (E°). Spontaneity under standard conditions requires a positive Ecell; kinetics and solvent effects can still influence the rate and extent of the reaction.

Common examples include zinc displacing copper from copper(II) sulfate: Zn + CuSO4 → ZnSO4 + Cu. Iron can displace copper in a similar reaction: Fe + CuSO4 → FeSO4 + Cu. Halogen displacement is another type, such as chlorine displacing bromide: Cl2 + 2KBr → 2KCl + Br2.

Single-displacement reactions have applications in metallurgy, electrochemistry, and qualitative analysis, where reactivity trends guide metal extraction and solution testing. Limitations include that displacements do not occur if the entering element is less reactive, and kinetics, temperature, and solvent conditions can affect feasibility or reversibility of the reaction.