SINGLE DISPLACEMENT REACTIONS
In this type of reaction, one element displaces (replaces) another in a compound. This happens in two situations:
1. When a metal displaces a metal. e.g.
Li(s) + NaCl(aq) ® LiCl(aq) + Na(s)
2. A non-metal displaces a non-metal.
F2(aq) + 2KI(aq) ® I2(aq) + 2KF(aq)
In most single displacement reactions there is an element and an ionic compound as reactants.
The general pattern is:
A + BC ® AC + B
element A displaces element B
A and B are elements
BC and AC are compounds
e.g. Cu(s) + 2AgNO3(aq) ® 2Ag(s) + Cu(NO3)2(aq)
2Li(s) + 2H2O(l) ® H2(g) + 2LiOH(aq)
Whether or not one element can displace another element in a compound depends on the relative reactivities of the two elements.
e.g. Cu can replace Ag in the reaction above because Cu is more reactive then Ag.
A more reactive element can displace a less reactive element from a compound.
Metals are arranged in order of decreasing reactivity in the activity series. Halogens are also arranged in order of decreasing reactivity in the halogen displacement series. The activity series and the halogen displacement series are used to predict single displacement reactions.
Lithium Each metal will displace any metal that appears below it.
Potassium These metals dislpace hydrogen from H2O and acids
Zinc These metals displace H from acids
Copper These metals do not
Mercury react with most acids or bases
Fe(s) + CuSO4(aq) ® FeSO4(aq) + Cu(s)
Copper appears below iron, therefore iron will replace it.
Cu(s) + FeSO4(aq) ® No Reaction
Iron is above copper, therefore the reaction will not occur.
Each element in the halogen series will replace any halide ion below it.
Cl2(aq) + 2NaBr(aq) ® Br2(aq) + 2NaCl(aq)
Bromine appears below chlorine, therefore chlorine will replace it.
Br2(s) + 2NaCl(aq) ® No Reaction
Chlorine is above bromine, therefore the reaction will not occur.
PREDICT THE PRODUCTS OF THE FOLLOWING REACTIONS:
1. Zn(s) + Pb(NO3)2(aq) ®
2. Pb(s) + Zn(NO3)2(aq) ®
3. Al(s) + NiCl2(aq) ®
4. Mg(s) + H2SO4(aq) ®
5. Br2(aq) + CaCl2(aq) ®
7.5 - Single-Replacement Reactions
One element replaces another in a compound.
A + BC --> AC + B (positive ion is replaced)
D + BC --> BD + C (negative ion is replaced)
• A reactive metal will replace any metal found below it in the activity series (Table 7.2, pg 155).
• Compare the reactivity of Cu, Zn, and Mg in HCl(aq).
Fe(s) + CuCl2(aq) --> FeCl2(aq) + Cu(s)
Try Question # 7 on page 155.