Double replacement

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A double replacement or double displacement is a reaction where two cations exchange anions or vice versa.

These reactions are usually in equilibrium; they proceed to completion in the following cases:

  • One of the resulting products is insoluble and precipitates (e.g. barium sulfate);
  • One of the resulting products is a poorly dissociated, mostly molecular compound (e.g. water);
  • One of the resulting products is volatile and is distilled off the mixture (e.g. nitric acid);
  • One of the resulting products is unstable and decomposes into non-ionic products such as gases and water (e.g. carbonic acid);