Combustion, oxidation and thermal decomposition

In a nutshell

Combustion involves burning a substance in oxygen, oxidation is when a substance gains oxygen and thermal decomposition is when a substance breaks down due to heat. In this summary you will learn more about these reactions with examples.

Equation

Reactants		Products
$hydrocarbon \ +\ oxygen$	$\rarr$	$carbon\ dioxide\ +\ water$
$metal\ +\ oxygen$	$\rarr$	$metal\ oxide$

Combustion

Combustion is a type of reaction which involves burning a substance in oxygen. Combustion reactions release a lot of energy, mostly in the form of heat energy but it can also be released as light energy.

Three things are needed for a combustion reaction to take place:

Fuel
Oxygen
Source of heat

Example

Burning fuels involves combustion reactions. Fuels contain hydrocarbons (which are molecules made up of hydrogen and carbon atoms only). With a good supply of oxygen and heat, hydrocarbons burn in oxygen to produce water and carbon dioxide.

$hydrocarbon \space + oxygen \rightarrow water \space + carbon \space dioxide$

Oxidation

An oxidation reaction involves a substance reacting with oxygen and thereby gaining oxygen.

Combustion is a type of oxidation reaction. Several types of metals react with oxygen in the air when heat is applied to product metals oxides. Rust is formed via an oxidation reaction: iron reacts with oxygen to produce iron oxide (rust).

Example

When heat is applied, magnesium can react with oxygen in the air to form magnesium oxide.

$magnesium \space + oxygen \rightarrow magnesium \space oxide$
$2Mg(s) \space + \space O_2(g) \rightarrow 2MgO(s)$

Thermal decomposition

Thermal decomposition is a process whereby a substance breaks down when heat is applied.

Not every substance can undergo thermal decomposition; most substances melt when heated.

Example

Calcium carbonate undergoes thermal decomposition to produce calcium oxide and carbon dioxide.

$calcium \space carbonate \longrightarrow calcium \space oxide \space+ \space carbon \space dioxide$

$CaCO_3(s) \rightarrow CaO(s) \space+ \space CO_2(g)$