Gibbs Free energy

  • Thread starter Coco12
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  • #1
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Homework Statement




When gaseous nitrogen and hydrogen are converted to gaseous ammonia, then delta G equals: -16.64Kj/mol

3h2+ n2=2nh3
Using the s values , calculate the delta h for the formation of ammonia

Homework Equations



Delta s for:
H2:130.6
N2:191.5
Nh3:192.5

T= 298

The Attempt at a Solution



Delta h= delta G + T delta s

The ans is 46.2 kj/mol for NH3

I understand how to get the delta s values
However how did they get 46.2

In the ans, they multiplied delta g by 2
And then after adding it to the T delta s
They got 92.3 Kj and divided it by 2 mols to get 46.2

My question is why are they multiplying delta G by 2?
 

Answers and Replies

  • #2
Borek
Mentor
28,499
2,913
Most likely data given

delta G equals: -16.64Kj/mol
is per mole of ammonia produced, not per so called "mole of reaction". Thus, as in a "mole of reaction" two moles of ammonia are made, you need to multiply by 2.

But if that's the case it should be clearly spelled out what the data refers to, otherwise question is ambiguous. Nothing wrong with listing values per mole of substance or mole of reaction, as long as it is clear which one is given.
 

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