Question

Calculate ΔH∘ in kilojoules for the reaction of ammonia (ΔH∘f=−46.1 kJ/mol) with O2 to yield nitric oxide NO (ΔH∘f=91.3 kJ/mol) and H2O(g) (ΔH∘f=−241.8 kJ/mol), a step in the Ostwald process for the commercial production of nitric acid.

Answer 1

write a reaction and a balance it (because you need the coefficients

\(\Delta H^0_{rxn}= \Sigma v_i\Delta H^o_{products}-\Sigma v_i\Delta H^o_{reactants}\)

this basically means "products - reactants", but you need to multiply their individual \(\Delta H^o\) by their stoichiometric coefficients first.

Answer 2

I tried that, I got the balanced equation 2NH3 + 3O2 --> 2NO + 3H2O and then I multiplied 2(-46.1) - {2(91.3) + 3(-241.8)} and ended up with 450.6. When I typed that in, it told me it was incorrect

Answer 3

it's products - reactants, you did it the other way around
[2(91.3) + 3(-241.8)] - [2(-46.1)]

Answer 4

Oh, ok. I redid it that way, and got -450.6, but it still says it's incorrect :P

Answer 5

maybe it's because of sig figs?

Answer 6

I don't know, it just says to express it using one decimal place

Answer 7

ohh the equation isn't balanced

Answer 8

Darn it! I thought I had it :P

Answer 9

not quite hah

Answer 10

Haha well thank you

Answer 11

no probrem !