Types of Chemical Reactions

Types of Chemical Reactions There are only five (5) different types of

chemical reactions:1) Double Replacement2) Single Replacement3) Synthesis/Formation4) Decomposition5) Combustion

Reaction Type 1 – Double Replacement

Occur between two ionic compoundsDoes not happen with covalent compounds

Involves an exchange of cations (positive ions)

The cation of one compound trades places with the cation of another compound to form two new compounds

Double Replacement - Characteristics

occur in solution when the compounds are in an aqueous state (aq)reactants are either aqueous to begin with,

or solid compounds dissolved in water to form an aqueous solution of ions

in order to drive the reaction, one of the products must be removed from the aqueous solution

this can occur via one of three ways:

Double Replacement - Characteristics

1) Formation of a precipitate (an insoluble solid forms in the solution)

i.e.:

AgNO3 (aq) + NaCl (aq) = NaNO3 (aq) + AgCl (s)

Solid silver chloride is formed as precipitate and comes out of the solution

Double Replacement - Characteristics

2) Formation of a gas i.e.:

FeS (aq) + 2HCl (aq) = H2S (g) + FeCl2 (aq)

Hydrogen sulfide gas is formed and comes out of the solution

Double Replacement - Characteristics

3) Water is formed when a hydrogen cation unites with a hydroxide anion

i.e.:

NaOH (aq) + HCl (aq) = HOH (l) + NaCl (aq)

Water (HOH) is formed and comes out

of the solution

Identifying a Double Replacement Reaction

Double replacement reactions always have two ionic compounds on the REACTANTS side AND on the PRODUCTS side of an equation

*Two compounds react to form two new compounds*AB + CD CB + AD

○ A & C are cations, B & D are anions○ A & C switch places

Reaction Type # 2 – Single Replacement

Single Replacement Reactions: Characteristics: Atom (s) of a lone element replace the

atom (s) of an element in a compoundMetals replace metals (or cations replace

cations)Non-metals replace non-metals (or anions

replace anions)

Single Replacement Reactions: Characteristics: Metal Cation Replacement:

For the reaction:

A + BC B + AC

A and B are cationsA “replaces” B in the compound

Single Replacement Reactions: Characteristics: Non-metal Anion Replacement:

For the reaction:

D + EF ED + F

D & F are anionsD “replaces” F in the compoundNon metal replacements usually involve

halogens

Restrictions on Single Replacement Reactions Activity Series:

A characteristic of metals and halogens referring to their reactivity

Determines whether or not a single replacement reaction will occur or not

Metals: on page 155 (table 7-2) there is an activity series of metals arranged in order of decreasing activity

Non-metals (Halogens) : as you move down the group on the periodic table activity decreases

Restrictions on Single Replacement Reactions A single replacement reaction WILL

NOT OCCUR if the reactivity of the pure element reactant is less than that of the compound reactanti.e.:

Sn (s) + NaNO3 (aq)

no reaction b/c tin is less reactive than sodium

Restrictions on Single Replacement Reactions A single replacement reaction WILL

OCCUR if the reactivity of the pure element reactant is greater than that of the compound reactanti.e.:

Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

Reaction occurs because the reactivity of zinc is higher than hydrogen

Identifying Single Replacement Reactions Single replacement reactions ALWAYS

have 1 lone element and 1 compound on the reactants side and the products side

Reactants will always be:1 lone element + 1 compound

Products will always be:1 lone element + 1 compound

Reaction Type #3 - Decomposition Occurs when a single compound breaks

down into two or more components Energy is required for them to occur Reactants will always be:

1 compound Products will always be:

ALWAYS more products than reactants2 components (either compounds or elements)

i.e.: AB A + B

Decomposition Example: One unit breaks

down into its component parts

i.e. – The marriage of Brad Pitt and Jennifer Aniston breaks into the single Brad Pitt and the single Jennifer Aniston

Reaction Type #4 – Synthesis/Formation Occurs when two or more components

come together to form one compound Energy is released when these reactions

occur Reactants will always be:

ALWAYS more reactants than products!2 or more components (either elements or

compounds) Products will always be:

1 single compound i.e.:

A + B AB

Synthesis/Formation Example

Two individual components coming together to form one unit

i.e. – single Robert Pattinson and a single Kristen Stewart come together to form a totally awesome Twilight couple OMG OMG LOL ECLIPSE! LIKE TOTALLY AWESOME!

Special Cases for Decomposition & Synthesis/Formation Reactions Decomposition and Synthesis/Formation

Reactions are opposite processes (duh) Special Case #1:

A non metal oxide + water combine to form an acid ○ i.e.: SO3 + H2O H2SO4

AND an acid will decompose to form a non-metal oxide + water○ i.e.: H2SO4 SO3 + H2O

Special Cases for Decomposition & Synthesis/Formation Reactions Special Case #2

A metal oxide + water combine to form a metal hydroxide ○ i.e.: CaO + H2O Ca(OH)2

A metal hydroxide will decompose into a metal oxide + water○ i.e.: Ca(OH)2 CaO + H2O

Special Cases for Decomposition & Synthesis/Formation Reactions Special Case #3:

All carbonates decompose into carbon dioxide and an oxide

i.e.: CaCO3 CaO + CO2

Vice versa for synthesis/formation reactions

Special Case #4:All chlorates decompose into oxygen and a

binary salti.e.: KClO3 KCl + O2

Vice versa for synthesis/formation reactions

Reaction Type #5 - Combustion Also known as BURNING Hydrocarbon

Compound composed of only carbon and hydrogen and sometimes oxygen

Reactants will always be:Hydrocarbon + oxygen

Products will always be:Carbon dioxide + water

i.e.:C6H6 + O2 CO2 + H2O