Chemical Reactions

SCH 3U Unit 2 Part 3

Classifying Reactions

• Most chemical reactions can be grouped or organized into 5 categories.

• Synthesis• Decomposition• Single Displacement• Double Displacement• Combustion

Synthesis Reactions

• A synthesis reaction occurs when two or more small substances combine to produce a larger substance.

A + B AB

Only 1 product!

Types of Synthesis

• Two elements may combine to form a compound:

hydrogen + oxygen water

2H2 + O2 2H2O

Remember to criss-cross new subscripts!

• Two compounds may combine to form a larger compound:

carbon dioxide + water carbonic acid

CO2 + H2O H2CO3

Types of Synthesis

General Synthesis Reactions

• Nonmetal oxide + water oxyacid

• Metal oxide + water metal hydroxide

Na2O + H2O 2NaOH

SO2 + H2O H2SO3

Synthesis of Acids and Bases

Na2O + H2O NaOH

MgO + H2O Mg(OH)2

SO2 + H2O H2SO3

Cl2O5 + H2O HClO3

Applications of Synthesis

• Rusting• Iron combines with oxygen in the air to form iron (III) oxide or rust.

The rust then flakes away, exposing new metal underneath to the oxygen.

• Acid Rain• Non-metal oxides found in the air due to pollution

combine with water to form acids. These acids fall to the ground as acid rain.

Applications of Synthesis

• Polymerization • Small molecules are linked together to form long-chain molecules called

polymers.

Applications of Synthesis

Decomposition Reactions

• A decomposition reaction occurs when one larger substance breaks up into two or more smaller substances.

AB A + B

Only 1 reactant!

Decomposition reactions are the opposite to synthesis!!

Types of Decomposition• A compound may decompose to produce two

elements

water hydrogen + oxygen

2H2O 2H2 + O2

Remember to make the seven sisters diatomic!

• A large compound may decompose to produce two smaller compounds

Types of Decomposition

potassium potassium + oxygen chlorate oxide

KClO3 KCl + O2

General Decomposition Reactions

• Metal carbonates decompose to produce a metal oxide and carbon dioxide

CaCO3 CaO + CO2

calcium calcium + carboncarbonate oxide dioxide

Applications of Decomposition

• Production of Hydrogen• The decomposition of water is used in the production of hydrogen for

hydrogen fuel cells.

• Return of atmospheric carbon• Decomposition reactions release carbon dioxide back into the atmosphere to

re-enter the carbon cycle.

Applications of Decomposition

• Pg 125 # 7-10• Pg 127 # 21-30• Pg 132 #13, 15, 16• Pg 134 # 31-40

• Pg 136 # 2, 4, 7, 8, 15

Time to get to Work