Single replacement reactions example

Examples of Single Replacement Reactions

In chemistry, there are three basic types of reactions, which include addition reactions, decomposition reactions, and displacement reactions. Among them, this Buzzle article comes forward to discuss in length about a type of displacement reaction called single replacement reaction, accompanied by various examples.
Did You Know?
To protect structures made of iron from corroding, a more reactive metal like zinc is added to it. It reacts with the environment and corrodes itself, while the iron is protected. Such metals are aptly given the name "sacrificial metal."

In chemistry, the compounds that take part in a chemical reaction are called reactants, whereas the compounds that are formed after a chemical reaction are called products. Reactants are physically and chemically distinct from the products that they make. A chemical reaction can be given as:

A + B C + D

As a rule, the reactants A and B are written on the left-hand side, and their products are written on the right-hand side of the arrow (signifies a chemical reaction).

In a displacement reaction, there is displacement of one of the reactants by another reactant. Usually, these reactions take place between a metal and non-metal that are joined by an ionic bond. Displacement reactions can be further classified into single replacement reaction and double replacement reaction. In single replacement reactions, one ion or an atom of an element is displaced by another ion or atom (discussed in detail below). In a double replacement reaction, there is interchanging of ions or atoms between the reactants.

Single Replacement Reactions

Single replacement reactions or single displacement reactions involve the replacement of an atom or an ion from one compound by a more reactive compound. This type of a reaction can be depicted in the following manner:

A + B-C B + A-C

Here, A is a more reactive compound as compared to B; B is, therefore, displaced from the compound B-C to give the products B and A-C. A and B are usually metals (give off electrons) or a positively charged hydrogen. C is usually a non-metal or an anion (accepts electrons) and usually considered as a spectator ion as it doesn't take part in the reaction.

How are some compounds more reactive than others?
Reactivity of an element (usually metals) can be determined by the ease with which it gives off an electron. The order their reactivity can be given as follows:

K > Na > Li > Sr > Ca > Mg > Al > Zn > Cr > Fe > Ni > Sn > Pb > H > Cu > Ag
Note: Hydrogen is given here for comparison.

In our surroundings, we encounter some examples of single replacement reaction.

In the extraction of iron from its ore, ferric oxide is heated with carbon. Carbon displaces iron at very high temperature, and then elemental iron is formed.

2Fe2O3 + 3C 4Fe + 3CO2

There are two types of single replacement reactions:
Cation Replacement Reactions

In this type of reaction, a cation (positively charged ion) replaces another cation that is present in the compound.

X + [Y]+[Z] - Y + [X]+[Z]-

Here, one cation X+ replaces another cation Y+.

These reactions are considered as redox reactions as there is simultaneous reduction of one reactant, and there is oxidation of the other reactant. X+ takes up electrons and undergoes reduction, whereas Y+ gives off its electron and undergoes oxidation reaction.

Cation Replacement Reaction Examples

Zn(s) + 2HCl(aq) ZnCl2 + H2

Breaking down this reaction, we get;

Zn + HCl Zn+Cl + H0
Zn+Cl + HCl + H0 ZnCl2 + H2(g)

Here, zinc is more reactive than hydrogen. It displaces hydrogen from hydrochloric acid by undergoing oxidation itself, and reducing hydrogen cation to form zinc chloride.

Ca(s) + H2O Ca(OH)2 + H2(g)

Breaking down this reaction, we get;

Ca + H2O Ca+(OH) + H0
Ca+(OH) + H0 + H2O Ca(OH)2 + H2

Here, calcium is more reactive than hydrogen. It displaces hydrogen from water to form calcium hydroxide. Calcium itself undergoes oxidation, and the hydrogen cation is reduced.

Fe(s) + CuSO4(aq) FeSO4 + Cu(s)

Here, iron is more reactive than copper. It displaces copper from copper sulfate by undergoing oxidation itself and reducing copper cation to form ferrous sulfate. As copper is precipitated out of the solution, it loses its bright blue color.

Zn(s) + AgNO3(aq) 2 Ag(s) + Zn(NO3)2(aq)

Breaking down this reaction, we get;

Zn + AgNO3 Zn+NO3 + Ag0
Zn+NO3 + Ag0 + AgNO3 Zn(NO3)2+ 2Ag0

Here, zinc is more reactive than silver. It displaces silver from silver nitrate by undergoing oxidation itself and reducing silver cation to form zinc nitrate.

Anion Replacement Reaction

In this type of reaction, an anion (negatively charged ion) replaces another anion that is present in the compound.

P + [Q]+[R]- R + [Q]+[P]-

Here, one anion P- replaces another anion R-.

These reactions are also considered as redox reactions as there is a simultaneous reduction of one reactant and oxidation of the other. P takes up electrons and undergoes reduction, whereas R- gives off its electron and undergoes an oxidation reaction.

Halogens are highly electronegative elements. These elements take up electrons rather easily, and the ease with which they take up electrons refers to the reactivity of these elements. The reactivity of halogens is given below:

F > Cl > Br > I

Anion Replacement Reaction Examples

Cl2(g) + NaBr(aq) 2NaCl(aq) + Br2(g)

Breaking down this reaction, we get;

Cl2 + NaBr NaCl + Br- + Cl0
NaCl + Br- + Cl0 + NaBr 2NaCl + Br2

As chlorine is more reactive, it replaces bromine from sodium bromide. It undergoes reduction reaction and oxidizes the bromide anion to form sodium chloride.

Br2(g) + NaI(aq) 2NaBr(aq) + I2(g)

Breaking down this reaction, we get;

Br2 + NaI NaBr + Br- + I0
NaBr + Br- + I0 + NaI 2NaBr+ I2

As bromine is more reactive, it replaces iodine from sodium iodide. It undergoes reduction reaction and oxidizes the iodide anion to form sodium bromide.

Br2(g) + 2KI(aq) 2KBr(aq) + I2(g)

Breaking down this reaction, we get;

Br2 + KI KBr + Br- + I0
KBr + Br- + I0 + KI 2KBr+ I2

As bromine is more reactive, it replaces iodine from potassium iodide. It undergoes reduction reaction and oxidizes the iodide anion to form potassium bromide.

Both anion and cation replacement reactions are irreversible reactions, where the more reactive ion or atom replaces the less reactive one.