For any chemical reaction, thermodynamics dictate the conditions at which it will occur and the relative amount of products and unconverted reactants. In some reactions, all the reactants are converted into products and the reaction is 100% complete. Other reactions are limited by chemical equilibrium and only a portion of the reactants are converted. The relative amount of products and reactants at equilibrium depends upon the operating conditions and this is dictated by thermodynamics. Note that thermodynamics will not predict the amount of time required to reach equilibrium or to complete a given chemical reaction.