Single replacement scheme

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A Single replacement reaction (also known as composition reaction) is when one element replaces another element in a compound.

There are two different possibilities:

[edit] Cation replacement

One cation replaces another. A cation is a positively charged ion. When it is written in generic symbols, it is:

AX + Y → YX + A

Element Y has replaced A (in the compound AX) to form a new compound YX and the free element A. This is an oxidation-reduction reaction wherein element A is reduced from a cation into the elemental form and element Y is oxidized from the elemental form into a cation.

Some examples are:

  1. Cu + 2AgNO3 → 2Ag + Cu(NO3)2
  2. Fe + Cu(NO3)2 → Fe(NO3)2 + Cu
  3. Ca + 2H2O → Ca(OH)2 + H2
  4. Zn + 2HCl → ZnCl2 + H2

[edit] Anion replacement

One anion replaces another. An anion is a negatively charged ion. Written using generic symbols, it is:

A + XY → XA + Y

Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. This is an oxidation-reduction reaction wherein element A is reduced from the elemental form into an anion and element Y is oxidized from an anion into the elemental form.

Some of the only examples that involve halogens are here, so here are the two examples:

  1. Cl2 + 2NaBr → 2NaCl + Br2
  2. Br2 + 2KI → 2KBr + I2


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