Types of Chemical Reactions

Chemical ReactionsA chemical reaction has occurred

when the starting substances (reactants) recombine to form ending substances (products).

The reactants will, most often, have different chemical and physical properties than the products.

Evidence of a chemical reaction can include (but is not limited to): bubbles, flames, change of color, change of state, precipitate.

Basic Types of Chemical ReactionsSynthesis (or combination)DecompositionSingle ReplacementDouble ReplacementCombustion

Synthesis (Combination)Just like the name implies, a new

substance is formed from two or more reactants.

The typical chemical equation will appear in the form of

A + B → ABA and B can be single elements or

molecules.Example:

2H2 + O2 → 2H2O

DecompositionAgain, as the name implies, this type

of reaction involves breaking reactants down into simpler substances.

In many ways, it is the opposite of a synthesis reaction.

The typical chemical equation will appear in the form of

AB → A + BExample:

2KClO3 → 2KCl + 3O2

Single ReplacementIn this type of reaction a single, reactive

metal will replace a less reactive metal already bonded in an ionic compound.

The typical chemical will appear as A + BC → B + AC

Example: Cu + 2AgNO3 → 2Ag + Cu(NO3)2

You will need to use the activity series to determine whether this type of reaction will take place.

Activity SeriesThe only time a single replacement will

take place is when the free metal is more reactive than the metal cation bonded in the ionic compound.

This reactivity is based on ionization energy. A metal with a lower ionization energy is more reactive than one with a higher ionization energy.

You will need to use the activity series to determine which metals are more reactive than others.

Activity SeriesName Symbol

Decreasing reactivity

Lithium Li

Potassium K

Calcium Ca

Sodium Na

Magnesium Mg

Aluminum Al

Zinc Zn

Iron Fe

Lead Pb

(Hydrogen) H

Copper Cu

Mercury Hg

Silver Ag

A metal high on the table is more reactive and can replace a metal lower on the table. A metal lower on the table CANNOT replace a metal higher on the table.

Double Replacement Reactions

In this type of reaction, already bonded metal cations basically switch places with one another and bond with the already bonded nonmetal anions.

These reactions usually take place in aqueous solution.

The typical chemical equation will appear as

AB + CD → AD + CBExample:

CaF2 + 2NaNO3 → Ca(NO3)2 + 2NaF

Double Replacement Reactions

Usually produce bubbles, a precipitate, or a molecular compound such as water.

In order to occur, one of the following is usually true.◦One of the products is only slightly

soluble and precipitates.◦One of the products is a gas.◦One product is a molecular

compound such as water.

Predicting PrecipitatesWhen a precipitate is formed, the

precipitate can be predicted by using rules of solubility or a solubility table.

Remember, an insoluble substance will not dissolve in water and will therefore precipitate.

In a chemical reaction, a down arrow (↓) is usually written after the formula for the precipitate in order to indicate the precipitate.

Solubility Rules

Acid – Base Double ReplacementAn acid, for now, is defined as a

substance that produces a hydrogen ion in solution. We will recognize an acid as an ionic compound that starts with H.

Example: HCl, H2SO4

A base, for now, is defined as a substance that produces a hydroxide ion in solution. We will recognize a base as an ionic compound that ends with –OH.

Example: NaOH, Ca(OH)2

Acid – Base D.R. ReactionWhen an acid and a base react,

in a double replacement reaction, the products formed will be an ionic compound (salt) and water.

Example: 2NaOH + H2SO4 → Na2SO4 + 2H2O

base

wate

r

Ionic

salt

aci

d

Combustion ReactionIn a combustion reaction, a

hydrocarbon burns in oxygen. The products formed are always carbon dioxide and water.

The typical format for this reaction is

CxHy + O2 → CO2 + H2OExample:

CH4 + 2O2 → CO2 + 2H2O

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