Classifying Chemical Reactions

Types of Reactions

There are literally millions of chemical reactions that occur every day.

Chemists have defined five main categories of chemical reactions: combustion, synthesis, decomposition, single displacement, and double displacement.

Combustion Reactions

If you have ever observed something burning, you have observed a combustion reaction.

Our definition states that a combustion reaction occurs when a substance reacts with oxygen to produce energy in the form of heat and light.

CxHy+O2 CO2+H2O

Combustion

CH4 + 2O2 CO2 + 2H2O

The burning of a substance in O2 to

produce heat

Hydrocarbons (CxHy) always form

CO2 and H2O

Synthesis

the combination of 2 or more substances to form a compound

only one product forms

Basic form:

A + B AB2P + 3Br2 2PBr3

Decomposition Reactions

A decomposition reaction is just the reverse of a synthesis

Instead of two substances coming together to form a third, a decomposition reaction occurs when one substance breaks down, or decomposes, into two or more substances

Most decomposition reactions require the use of heat, light, or electricity.

Decomposition

a compound breaks down into 2 or more simpler substances

only one reactant

Basic form:

AB A + B2H2O2 2H2O + O2

The Activity Series

We can predict which metal will replace another using the diagram shown which lists metals according to how reactive they are

A metal will replace any less active metal.

Single Replacement

one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-) Basic form:

A + BC AC + BZn + 2HCl ZnCl2 + H2

Double Replacement

ions in two compounds “change partners”

cation(+) of one compound combines with anion(-) of the other

Basic form:

AB + CD AD + CB

2KOH + CuSO4 K2SO4 + Cu(OH)2

Double Replacement

A double replacement reaction takes place if a precipitate, water, or a gas forms when two ionic compounds in solution are combined.

A precipitate is an insoluble compound that comes out of solution during this type of reaction.