How much heat is absorbed/released when 20.00 g of NH3 (g) (17.0307g/mol) react in the presence of excess O2 (g) to produce NO (g) and H2O (l) according to the following chemical equation? 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (l) ΔH° = 1168 kJ

342.8 kJ are absorbed

Explanation:

In the reaction:

4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (l) ΔH° = 1168 kJ

As ΔH > 0, the heat is absorbed. Also, when 4 moles of NH3 are involved in the reaction, there are absorbed 1168 kJ.

Having this in mind, moles of NH3 in 20.00g are:

20.00g * (1mol / 17.0307g) = 1.174 moles

Thus, 1.174 moles of NH3 absorbed:

1.174 moles * (1168 kJ / 4 moles) = 342.8 kJ are absorbed.