If 1 g of hydrogen combines completely with 8 g of oxygen to form water, how many grams of hydrogen does it take to combine completely with 64 g of oxygen?

The balanced chemical reaction would be:

2H2 + O2 = 2H2O

We are given the amount of oxygen to react with hydrogen. To determine the amount of hydrogen needed for the oxygen to completely react, we use the balanced reaction to relate the substances. We do as follows:

64 g O2 (1 mol / 32 g) (2 mol H2 / 1 mol O2) (2.02 g / 1 mol) = 8.08 g of hydrogen gas needed