Single displacement reaction
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A single-displacement reaction is when one element appears to move out of one compound and into another. This is usually written as
- A + BX → AX + B
This will occur if A is more reactive than B. You can refer to the activity series to be sure of this.
A and B must either be different metals (hydrogen's behavior as a cation renders it as a metal here), in which case X represents an anion. However, A and B may also be halogens, in which case X represents a cation. In either case, when AX and BX are aqueous compounds (which is usually the case), X is a spectator ion.
Due to the free state nature of A and B, all single displacement reactions are also oxidation-reduction reactions. When A and B are metals, A is always oxidized and B is always reduced. Since halogens prefer to gain electrons, A is reduced (from a 0 to −1) and B is oxidized (from −1 to 0) when A and B represent those elements.
A and B may not have the same charge when ions are formed therefore some balancing of the equation may be necessary. For example the reaction between silver nitrate (AgNO3) and zinc (Zn) forms silver (Ag) and zinc nitrate (Zn(NO3)2).
- 2 AgNO3(aq) + Zn(s) → 2 Ag(s) + Zn(NO3)2(aq)
All simple metal with acid reactions are single displacement reactions. For example the reaction between magnesium (Mg) and hydrochloric acid (HCl) forms magnesium chloride (MgCl2) and hydrogen (H2).
- Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
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