When 3.54 grams of phosphorus react with excess oxygen gas to produce diphosphorus pentoxide, the percent yield is 84.1%. What was the actual yield of the reaction? 4P 5O2 yields 2P2O5

The atomic mass for phosphorus is 31. So the molar mass of P is 3.54/31=0.114 mol. And according to the reaction equation, the ratio of coefficient is equal to the mole number. So the theoretical mass of P2O5 is 8.094 g. The actual yield is 6.807 g.