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.

 

 

 

 

 

 

ACTIVITY SERIES

Lithium Each metal will displace any metal that appears below it.

Cesium

Rubidium

Potassium These metals dislpace hydrogen from H2O and acids

Barium

Strontium

Calcium

Sodium

Magnesium

Aluminum

Zinc These metals displace H from acids

Iron

Nickel

Tin

Lead

Hydrogen

 

Copper These metals do not

Mercury react with most acids or bases

 

Silver

Gold

For example:

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.

 

 

HALOGEN SERIES

Each element in the halogen series will replace any halide ion below it.

Fluorine

Chlorine

Bromine

Iodine

For example:

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) ®

 

Review

7.5 - Single-Replacement Reactions

One element replaces another in a compound.

A + BC --> AC + B (positive ion is replaced)

or

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).

Our example:

Fe(s) + CuCl2(aq) --> FeCl2(aq) + Cu(s)

 

Try Question # 7 on page 155.