delta G,H, and S are state functions, in lame terms that just means you can pretty much mess with them any way you'd like! The gibbs free energy standard equation is delG = delH - TdelS. To find these values you do products-reactants, for delH = (2mol(90250J)) - 0. the standard enthalpies of formations of any element in its standard state is zero, thus no subtraction. delS = (2mol)(211J) - (192J+205J). products - reactants again. now plug these values into delG to get your change in free energy
delG= (2mol(90250J)) - (298K)((2mol*211J) - (192J+205J)) is your answer
