Cu to moles of Cu Mole ratio: Convert moles of Cu to moles of Ag produced Mole to mass: Convert moles of Ag to grams of Ag produced The complete balanced equation would be: For the mass to mole step, the mass of copper (16.00 g) would be converted to moles of copper by dividing the mass of copper by its molecular mass: 63.55 g/mol. Now that the amount of Cu in moles (0.2518) is found, we can set up the mole ratio. This is found by looking at the coefficients in the balanced equation: Cu and Ag are in a 1:2 ratio. Now that the moles of Ag produced is known to be 0.5036 mol, we convert this amount to grams of Ag produced to come to the final answer: This set of calculations can be further condensed into a single step: Further examples For propane (C3H8) reacting with oxygen gas (O2), the balanced chemical equation is: The mass of water formed if 120 g of propane () is burned in excess oxygen is then Stoichiometric ratio Stoichiometry is also used to find the right amount of one reactant to "completely" react with the other reactant in a chemical reaction – that is, the stoichiometric amounts that would result in no leftover reactants when the reaction takes place. An example is shown below using the thermite reaction, This equation shows that 1 mole of and 2 moles of aluminum will produce 1 mole of aluminium oxide and 2 moles of iron. So, to completely react with 85.0 g of (0.532 mol), 28.7 g (1.06 mol) of aluminium are needed. Limiting reagent and percent yield The limiting reagent is the reagent that limits the amount of product that can be formed and is completely consumed when the reaction is complete. An excess reactant is a reactant that is left over once the reaction has stopped due to the limiting reactant being exhausted. Consider the equation of roasting lead(II) sulfide (PbS) in oxygen () to produce lead(II) oxide (PbO) and sulfur dioxide (): To determine the theoretical yield of lead(II) oxide if 200.0 g of lead(II) sulfide and 200.0 g of oxygen are heated in an open container: Because a lesser amount of PbO is produced for the 200.0 g of PbS, it is clear that PbS is the limiting reagent. In reality, the actual yield is not the same as