An example of complex chemical reaction is:
CO2 +H2O CH2O + O2
That isn't a normal balanced equation, so it's hard for you to wrap your mind around, it's the generic biochem shorthand formula, CH2O, for carbohydrate, either fructose, or it's isomer glucose, or glucose's polymers -- gycogen, starch, and cellulose. You just stick numbers in depending on what the product is.