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.

Question

Quizplus · Accepted Answer

From the balanced reaction, we can see that 4 moles of ammonia react with 7 moles of oxygen to produce 6 moles of water. Therefore, the ratio of ammonia to water is 4:6 or 2:3.

First, we can calculate the mass of water produced: 
27.0 g / (18.015 g/mol) = 1.499 mol

That means the initial amount of ammonia must have been: 
(2/3) * 1.499 mol = 0.999 mol

Finally, we convert the amount of ammonia to mass: 
0.999 mol * 17.031 g/mol = 17.0 g, which is the initial mass of ammonia.

Consider the Following Reaction