Replacement Reactions

In contrast to synthesis combustion, and decomposition reactions, many chemical reactions are replacement reaction and involve the replacement of an element in a compound. These reactions are also called displacement reactions.

There are TWO types of replacement reactions SINGLE-REPLACMENT REACTIONS AND DOUBLE-REPLACMENT REACTIONS

The reaction between lithium and water is shown below. Its reaction is as follows: Lithium solid reacts with liquid water to produce lithium oxide and hydrogen gas Single Replacement

This chemical reaction shows that a lithium atom replaces one of the hydrogen atoms in a water molecule. A reaction in which the atoms of one element replace the atoms of another element is called a single-replacement reaction. A + BX  AX + B

The lithium and water reaction is one type of single-replacement reaction in which a metal replaces a hydrogen atom in a water molecule. Another type of single-replacement reaction occurs when one metal replaces another metal in a compound dissolved in water. For Example: Solid copper is mixed with Silver Nitrate to form solid silver and copper nitrate

NOTE: A metal will not always replace another metal in a compound dissolved in water because metals differ in their reactivities. Reactivity is the ability to react with another substance

METALS: Most Active Least Active ----------------------------------------------------- Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Pl Au HALOGENS: Most Active Least Active F Cl Br I https://www.youtube.com/watch?v=m55kgyApYrY

You can use the activity series to predict whether or not certain reactions will occur. A specific metal can replace any metal listed as “less active than it” in a compound. It cannot replace any metal listed as “more active”.

For example, copper atoms replace silver atoms in a solution of silver nitrate. However, if you place a silver wire in aqueous copper (II) nitrate, the silver atoms will not replace the copper. --------------------------------------------------- Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Pl Au The letters NR (no reaction) are commonly used to indicate that reaction will not occur! Ag(s) + Cu(NO3)2 (aq)  NR

A THIRD type of single-replacement reaction involves the replacement of a nonmental in a compound by another nonmetal. Halogens are frequently involved in these reactions. Like metals, halogens exhibit different activity levels as shown below: HALOGENS: Most Active Least Active ----------------------------------------------------- F Cl Br I

F2 (g) + 2NaBr (aq)  2NaF (aq) + Br2 (l) The most active halogen is Fluorine, the least active is iodine. A more reactive halogen replaces a less reactive halogen that is part of a compound dissolved in water. For example: Fluorine replaces bromine in water containing dissolved sodium bromide. However, bromine does not replace fluorine in water containing dissolved sodium fluoride! F2 (g) + 2NaBr (aq)  2NaF (aq) + Br2 (l) Br2 (g) + 2NaF (aq)  NR

Example Problems: Predict the products that will result when these reactants combine, and write a balanced chemical equation for each reaction: Solid iron reacts with aqueous copper(II) sulfide Diatomic liquid bromine reacts with aqueous magnesium chloride Solid magnesium reacts with aqueous aluminum chlroide

Practice Problems for you: Solid potassium reacts with aqueous zinc chloride Chlorine gas reacts with aqueous hydrofluoric acid (hydrogen monofluroide) Solid iron reacts with aqueous sodium phosphate CHALLENGE! Solid aluminum reacts with aqueous lead (II) nitrate