If 16 grams of O2 react with excess C2H6, how many grams of CO2 will be formed? The formula mass of O2 = 32 amu and the formula mass of CO2 = 44amu. The balanced chemical equation is 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g)