 In chapter 5, we learned to predict the products of a reaction and to balance the equation to find the ratio between the reactants. If we have a pile of screws, we don't know in what ratio they will be used until we know what they combine with. If we combine the screws with hinges, we see that they combine in a ratio of five screws to one hinge. Here we have a pile of ten bolts and ten nuts. If the bolts and the nuts combine in a one-to-one ratio, they will combine to form ten bolt-nut combinations. Both the bolts and the nuts will be completely used up. If the nuts and bolts, however, combine in a ratio of two nuts to one bolt, the nuts will be used up and will be able to form only five nut-bolt combinations and five bolts will be left over. In this chapter, you will learn to use the balanced chemical equation to predict the ratio in which the reactants combine, to find out which reactant is used up first, to predict the amount of product that's produced in the reaction, and to also calculate how much reactant may be left over at the end of the reaction. This is important if you're manufacturing the compound to sell. You'd like to have the yield of your product to be high and the amount of leftover starting material to be low. The calculations that you're going to do in this chapter are what chemists refer to as stoichiometry.