Question

What is a single replacement reaction?

Answer 1

In a single replacement reaction, one element is replaced by another in a compound. The general reaction is A + BC `rarr` AC + B, where A and B are metals. In order for one metal to replace another, it must be more reactive, as indicated by its place in the activity series of metals. A metal can replace a metal below it in the activity series.

Halogens can also replace other halogens (group 17/VIIA). The general equation is A + XY `rarr` XA + Y, where A and Y are halogens. In order for a halogen to replace another, it must be more reactive, and the order of reactivity is the same as the order of the halogens in group 17; `"F"`, `"Cl"`, `"Br"`, `"I"`.

Example 1. Single Replacement of a Metal

`"Fe(s)"` + `"CuSO"_4"`(aq) `rarr` `"FeSO"_4"`(aq) + `"Cu"`(s)

Because Fe is above Cu in the activity series of the metals, it is more reactive than Cu, and will replace it in a compound.

The reverse reaction will not occur, because Cu is below Fe in the reactivity series and is therefore less reactive.

`"Cu(s)"` + `"FeSO"_4"`(aq) `rarr` no reaction

Example 2. Single Replacement of a Halogen

`"Cl"_2"`(g) + `"2NaBr(s)"` `rarr` `"2NaCl(s)"` + `"Br"_2"`(l)

Because Cl is above Br in the halogen group, it is more reactive than Br, and will replace Br in the compound.

The reverse reaction will not occur, because Br is below Cl in the halogen group and is therefore less reactive.

`"Br"_2"`(l) + `"2NaCl(s)"` `rarr` no reaction