Exercise \(\PageIndex{1}\) If you reacted 14.7 g of Zn in the following reaction, what volume of H 2 gas, measured at STP, would be produced? Zn (s) + 2 HCl (aq) --> ZnCl 2 (aq) + H 2 (g) Answer 5.04 L. (0.225 moles) Exercise \(\PageIndex{1}\) What mass of O 2 gas is contained in a 3.85 L container at STP?. Answer 5.50 g. (0.172 moles) Exercise \(\PageIndex{1}\) How many liters of H 2 gas, measured at STP, is needed to produce 85.0 g of NH 3 ? 3 H 2 (g) + N 2 (g) --> 2 NH 3 (g) Answer 168 L. (7.48 moles)