Consider the following reaction: 4NH3 (g) 7O2 (g) → 4NO2 (g) 6H2O (l) Consider an experiment in which you react ammonia and oxygen. At the end of the experiment, you find that you produced 27.0 g of water, and 8.52 g of ammonia is left over. Calculate the initial mass of ammonia. Assume the reaction went to completion.

Answer: Initial mass of ammonia: 25,537g NH3

Explanation:

First we review the equation giving is balanced by checking the amount of each element before and after the arrow.

4NH3 (g) 7O2 (g) → 4NO2 (g) 6H2O (l)

We have 4 Nitrogen atoms on both sides

12 Hydrogen atoms on both sides

14 Oxygen atoms on both sides

Second we gather the information what we are going to use in our calculations.

Final Mass of H2O = 27g and Molecular Weigth = 18,015g/mol

Left Mass of NH3 = 8,52g and Molecular Weight = 17,031 g/mol

Third we start discoverying the amount of NH3 that reacted completely to generate 27g of H2, by using the giving equation and its respective molecular weights.

27g H2O x 1mol H20 / 18,015 gH20 x 4mol NH3 / 6 mol H20 x 17,031g NH3 / 1mol NH3 = 17,017g NH3

17,017g NH3 were consumpted to generate 27 g of H2, however, lets remember that there is NH3 left, that must be added to finally discover the original amount

17,017g + 8,52g = 25,537g NH3