In this question, we have to set up the properly balanced reaction first:
4 NH3 + 5 O2 -> 4 NO + 6 H2O
Now that the reaction is properly balanced, we can see that the molar ratio between NH3 and NO is 4:4, the same number of moles of NH3 will be the same number of moles of NO
We have:
15.8 grams of NH3, molar mass = 17g/mol
Let's find how many moles we have:
17.03g = 1 mol
15.8g = x moles
x = 0.93 moles of NH3, therefore we will also have 0.93 moles of NO being produced, but we have to know how much of mass does it represent, we will use NO molar mass, 30.01g/mol
30.01g = 1 mol
x grams = 0.93 moles
x = 27.91 grams of NO in 0.93 moles
27.91g is the theoretical yield
21.8g is the actual yield
The percent yield we can calculate with the following formula:
%yield = actual yield/theoretical yield
%yield = 21.8/27.91
%yield = 0.781
The percent yield is 78.10%