Question

4NH3 + 5O2 → 4NO + 6H2O
2NO + O2 → 2NO2
3NO2 + H2O → 2HNO3 + NO

In this process, the NO made in the last reaction is recycled back into the second reaction and used as a reactant. In the end, all of the NO produced is recycled back so that when the manufacturing process is complete, essentially no NO remains. If a chemist starts with 50.0 grams of NH3 and an excess of water and oxygen, what mass of nitric acid can be made

Answer 1

Here is a worked example of a single stoichiometry problem. Just follow the steps. The process is the same for a multiple step problem.
http://www.jiskha.com/science/chemistry/stoichiometry.html

Answer 2

Consider the following equation, which represents the combustion of ammonia.

4NH3(g) + 3O2(g) --> 2N2(g) + 6H2O(g)

How many moles of O2(g) is required to form 10 mol of H2O(g) is burned?