Question

Ammonia burns in oxygen to form nitrogen monoxide and water according to the following reaction. How much heat is released if 47.9g ammonia is completely reacted with oxygen? H rxn= -902 kJ

4NH3 (g) + 5O2(g) —->4NO (g) + 6H2O (g)

Answer 1

-635 J or -.635 kJ

Step-by-step explanation:

ΔHrxn= The change/difference in enthalpy between the products and reactants. Here the ΔHrxn tells us there is -902 kJ released per mole. So we can say we 4 mols of NH3 release -902 kJ. This can also be applied to the other compounds, where 5 mols of O2 release -902 kJ.

Keeping that in mind, we are looking for the heat released for 47.9g of NH3, let's convert grams > mols > kJ using the connection we made above.

1. We first need the molar mass of NH3 (17g) to convert to moles.

(47.9 g NH3) x
`(1 mol NH3)/(17g NH3)` x
`(-902 kJ)/(4 mol NH3)` = -635 J

2. If we need it in kJ, we can convert knowing that...

1000 J= 1 kJ

-635 J x
`(1 kJ)/(1000 J)`= -.635 kJ