We've seen that it's a simple matter of utilizing the stoichiometric coefficients of a reaction to relate the moles of one substance and the moles of another substance in a chemical reaction. But we also know that from the moles of a substance we can either go to the number of molecules that number of moles represents, using Avogadro's number, or we can go to the mass that number of moles represents by using the molar mass of that substance. So that means that in a certain number of calculations, we can get from any of these three values for any substance to any of these three values for some other substance. Right now, let's learn how to go from a mass of reactant to a mass of product. Once again, using methane, say that one gram of methane combusts completely. How many grams of water will be produced? This time, it is not as easy as utilizing a stoichiometric ratio. Even though one mole of methane produces two moles of water, it is not the case that one gram of methane produces two grams of water because every substance has a different mass. In order to do this calculation, we have to convert our mass into moles. This means dividing by the molar mass of methane, which is 16. This gives us 0.0625 moles of methane. From here, we can use the stoichiometric ratio, as we have a numerical quantity of methane molecules. Multiplying by the 2-to-1 ratio of water to methane gives us 0.125 moles of water. And finally, multiplying the moles of water by the molar mass of water will give us the mass of water produced, which will be 2.25 grams. Let's try one more. If 5 grams of hexane combust completely, what mass of water will be produced? Once again, let's convert from a mass of hexane to the moles of hexane using the molar mass of hexane, since from there we can multiply by the stoichiometric ratio to get the moles of water, which will be 5 times as much, given the 10-to-2 ratio, and then from the moles of water, we can convert to a mass of water by using the molar mass of water. And in this way, we can go from a mass of reactant, to the moles of that reactant, to the moles of a product, to the mass of that product, for any chemical reaction.