How do you write chemical equations for combustion reactions?

The combustion of octane ##C_8H_18## follows this reaction
##2C_8H_18 + 25O_2 -> 16CO_2 + 18H_2O##
A combustion reaction takes a hydrocarbon and burns it in oxygen to release carbon dioxide and water. A hydrocarbon is a molecule that contains carbon and hydrogen.
The basic equation looks like this.
The combustion of propane ##C_3H_8## follows this reaction
##C_3H_8 + 5O_2 -> 3CO_2 + 4H_2O##
The combustion of pentane ##C_5H_12## follows this reaction
##C_5H_12 + 8O_2 -> 5CO_2 + 6H_2O##
The combustion of octane ##C_8H_18## follows this reaction
##2C_8H_18 + 25O_2 -> 16CO_2 + 18H_2O##