in the first problem, what would happen if you multiply grams sn by 118.69 grams/mole sn?; does the physical form of the material matter for these calculations?; what are the conditions for all gases in these calculations?; why do the coefficients need to be correct?; why is it important to get the subscripts correct in the formulas?; how can you tell if all the ratios were set up correctly?; if a reactant is in excess, why do we not worry about the mole ratios involving that reactant?; what if hydrogen were left over?