Single-replacement reactions

Single-replacement reactions include reactions of the general form: A + BC AC + B

There are two types of single-replacement reactions:

1. Single-replacement reactions of metals
2. Single-replacement reactions of nonmetals

Single-replacement reactions involving metals

Based on experimental investigations, a tabulated list of metals, known as the Activity Series of Metals, summarizes the order of reactivity of metals. Use the activity series of metals to make predictions of single-replacement reactions involving metals. Do NOT memorize the activity series of metal.

When predicting the products of single-replacement reactions, the rule is

A reactive metal in the activity series will displace the ion of any metal lower on the list.

The reaction will not proceed if the above rule is not met.

Examples

Copper wire in a solution of silver nitrate

When a piece of copper wire, Cu (s), is submerged in a solution of silver nitrate, AgNO₃, a reaction occurs. Shiny needlelike crystals of silver form on the copper wire.

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

The above reaction fits the form

A + BC AC + B

where A = Cu, B = Ag⁺, C = NO₃^-.

The activity series of metal shows that Cu is higher on the activity series than Ag. Therefore, the above single-replacement reaction occurs because Cu is higher on the activity series than Ag. In other words, Cu is capable of displacing the Ag⁺ , which occurs lower of the activity series.

Penny reactions

Single-replacement reactions involving nonmetals

As with metals, the reactivity of nonmetals are not the same. Some nonmetals are more reactive than others. In particular, we will concentrate on the halogens.

More reactive halogens react with compounds containing ions of less active halogens.

The order of reactivity for halogens, with the most reactive halogen listed first, is:

F₂, Cl₂, Br₂, and I₂.

When predicting the products of single-replacement reactions of nonmetal, the rule is

The more reactive nonmetal will displace the nonmetal that is less reactive.

The reaction will not proceed if the above rule is not met.

Example

Bromine is prepared by reacting chlorine gas, Cl₂, with aqueous sodium bromide, NaBr.

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

The above reaction fits the form

A + BC AC + B

where A = Cl₂, B = Na⁺, and C = Br^-.

Cl₂ replaces the bromide ion, Br^- in NaBr because Cl₂ is more reactive than Br^-.

Content suitability

BCIT courses: CHEM 0011