Single Displacement

A single displacement reaction or substitution reaction is a common and important type of chemical reaction. A substitution or single displacement reaction is characterized by one element being displaced from a compound by another element.

The general form of a synthesis reaction is:

A + BC → AC + B

D + BC → BD + C

A reaction will occur if:
  • A is a metal or cation more reactive than metal or cation B
  • D is an anion or nonmetal more reactive than anion or non-metal C

A and B must be either:
  • Different metals (hydrogen's behavior as a cation renders it as a metal here), in which case C represents an anion; or
  • Halogens, in which case C represents a cation.

In either case, when AC and BC are aqueous compounds (which is usually the case), C is a spectator ion.

In the activity or reactivity series, the metals with the highest propensity to donate their electrons to react are listed first, and the most unreactive metals are listed last. Therefore a metal higher on the list is able to displace anything on the list below it

Metal Acticity Series

Eg

        Al (s) + Fe(NO3)2 (aq)

Since Al is above Fe in the activity series, it is more reactive. Therefore, Al will displace iron from the iron (II) nitrate.

        Al (s) + Fe(NO3)2 (aq) → Al(NO3)3 (aq) + Fe (s)

Always remember to balance....

        2 Al (s) + 3 Fe(NO3)2 (aq) → 2 Al(NO3)3 (aq) + 3 Fe (s)

Eg.

       Zn (s) + Mg(NO3)2

Since Zn is below Mg in the activity series, it is less reactive. Therefore, Zn will not displace Mg from the magnesium nitrate

       Zn (s) + Mg(NO3)2 →  

Non-metal Activity Series