MASTERING CHEMISTRY

Question

1.75 gg H2H2 is allowed to react with 10.5 gg N2N2, producing 2.05 gg NH3NH3.

What is the theoretical yield in grams for this reaction under the given conditions?

Express your answer to three significant figures and include the appropriate units.

Answer 1

The balanced chemical reaction is:

 

3H₂ (g) + N₂ (g) → 2NH₃ (g)

 

 

You have to first determine whether H₂ or N₂ is the limiting reagent as the theoretical yield of NH₃ is dependent upon the # of moles of the limiting reagent.

Now you have to use stoichiometry to perform these calculations. To convert grams to moles, we need the molar mass of H₂ (2 g/mol) and N₂ (28 g/mol). From the reaction, you can see that 3 moles of H₂ reacts to form 2 moles of NH₃, and 1 mole of N₂ reacts to form 2 moles of NH₃. The process is as follows:

 

g H2 → mol H2 → mol NH3

 

g N2 → mol N2 → mol NH₃

 

1.75 g H₂ x (1 mol H₂ / 2 g H₂) x (2 mol NH₃ / 3 mol H₂) = 0.583 mol NH₃

 

10.5 g N₂ x (1 mol N₂ / 28 g N₂) x (2 mol NH₃ / 1 mol N₂) = 0.75 mol NH₃

 

From above, you can see that H2 produces less NH3, therefore, it is the limiting reagent. The theoretical yield of NH3 is:

 

0.583 mol NH₃ x (17 g NH₃ / 1 mol NH₃) = 9.911 g NH₃