Consider the following equation:

Question

4NH3(g) + 5O2(g)----> 4NO(g)+6H2O(g)
a. How many liters of oxygen are required to react with 2.5 L NH3? Both gases are at STP
b. How many grams of water vapor can be produced from 25 L NH3 if both gases are at STP?
c. How many liters of NO can be produced when 25 L O2 are reacted with 25 L NH3? All gases are at the same temperature and pressure.

Answer 1

a and b can be solved by following the steps in the link below.
http://www.jiskha.com/science/chemistry/stoichiometry.html

c is a limiting reagent problem. Solve TWO stoichiometry problems and take the limiting reagent as the one producing the smaller value of product.
Post your work if you get stuck.
There is a shorter way to do it if you want to look into it. When ONLY gases are involved, you may use L as moles and make the coversions directly. For example,
2.5 L NH3 x (5 moles O2/4 moles NH3) = ??moles NH3.