[nextpauling]

I was wondering why we define the standard enthalpy, gibbs energy, etc of rxn with respect to the standard states (i.e. most stable pure form of reactant/product at T and 1 bar) and I arrived at the following explanation...by defining these standard states we can speak of a single change in state function for each reaction at a fixed T.  Even though in the lab our reactants and products may not begin/end in their standard states, we could in principle calculate the effects of bringing the reactants from and the products to their standard states and usually find that the error of assuming the standard thermo function change for our non-standard state reaction mixture is small.  Does this sound reasonable to anybody?