What is the word equation for a general combustion reaction?

Answer 1

Hydrocarbons (which are only hydrogen and carbon) require oxygen to combust, and they form water and carbon dioxide. So a general formula might look something like this:

CnHm + (m/4 + n)O2 → (m/2)H2O + nCO2

where n is the number of carbons in the hydrocarbon and m is the number of hydrogens. In hydrocarbon equations, it's very possible to have a fraction for the oxygen. Combustion reactions are one of few reactions where it's acceptable to do this. However, some teachers may still ask you to get rid of the fraction. To do this, multiply each compound's coefficient by two (or whatever the denominator is in oxygen's coefficient, but it will rarely be anything but two because the number of hydrogens, m, will almost always be even).

Answer 2

Reactant + Oxygen ----> Oxide(s) + heat

Above is a general formula for a combustion reaction. Every combustion reaction gives off energy. Depending on the reactants the oxide is formed.

For example, if we burn only Carbon containing coal, the product is Carbon dioxide :

C + O2 ----> CO2

If we burn Carbohydrates or Hydrocarbons, along with carbon dioxide, water is formed :

C2H6 + 4 O2 ----> 2 CO2 + 2 H2O

C6H12O6 + 6 O2 ----> 6 CO2 + 6 H2O

Depending on metal or non-metal burnt, products are also different :

2 Mg + O2 ----> 2 MgO

4 Na + O2 ----> 2 Na2O

S + O2 ----> SO2

4 P + 5 O2 ----> 2 P2O5