Combustion reactions

Combustion reactions occur between oxygen and almost anything else.

Generally, these are the reactions that we think of as “fire” but they can occur so slowly that we barely feel any warmth if any at all, and so quickly that they explode and then are finished.That means that the rusting of metal is combustion just as was the destruction of the Hindenburg is combustion.

Recognizing Combustion Reactions

Combustion reactions are easy to spot: they always have 2 reactants, one of which is oxygen. (Remember that oxygen is one of the HOFBrINCl's and therefore appears as O₂ not O.)

Completing Combustion Reactions

Most combustion reactions (at least those that occur in first year chemistry) involve hydrocarbons and perhaps a few other simple organic compounds. What that means is that probably everything your teacher burns (for real or on paper) will be made of carbon and hydrogen and perhaps some oxygen.

Competing these reactions is very straightforward. If the reactant includes hydrogen, the product will be water (H₂O). If the reactant contains carbon, the product will be carbon dioxide (CO₂). If the reactant contains both, then there will be two products (H₂O and CO₂). Extra oxygen in the reactant will NOT change the products. Here are a few examples (These reactions are NOT balanced, so that you can focus on the the identity of the products.)

Balancing Combustion Reactions 

Although balancing combustion reactions is not really different from balancing other types of reactions, there are some patterns you should learn to recognize. We'll look at 3 particular reactions.