are examples of decomposition reactions.

occur when a compound, usually one containing carbon, combines with the oxygen gas in the air. This process is commonly called . Heat is the most-useful product of most combustion reactions.

and the decomposition of hydrogen peroxide to form oxygen gas and water,

Combustion reactions always involve molecular oxygen O2. Anytime anything burns (in the usual sense), it is a combustion reaction. Combustion reactions are almost always exothermic (i.e., they give off heat). For example when wood burns, it must do so in the presence of O2 and a lot of heat is produced:

Classifying Synthesis, Decomposition, and Combustion Reactions

Classifying Synthesis, Decomposition, and Combustion Reactions

For example, simple hydrogen gas combined with simple oxygen gas can produce a more complex substance-----water!
The chemical equation for this synthesis reaction looks like:

reactant + reactant -------> product
To visualize a synthesis reaction look at the following cartoon:

In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.
In a decomposition reaction a more complex substance breaks down into its more simple parts.