Calculate Delta G & Delta H of N2+3H2=>2NH3

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SUMMARY

The discussion focuses on calculating the Gibbs free energy change (Delta G) and enthalpy change (Delta H) for the reaction of nitrogen and hydrogen forming ammonia, specifically N2 + 3H2 → 2NH3. The calculated Delta G is -16.64 kJ/mol, and the Delta H for the formation of ammonia is determined to be 46.2 kJ/mol. The calculation involves using the equation Delta H = Delta G + T * Delta S, where the Delta S values for H2, N2, and NH3 are provided. The multiplication of Delta G by 2 is necessary because the given Delta G value is per mole of ammonia produced, not per mole of reaction.

PREREQUISITES
  • Understanding of thermodynamic concepts such as Gibbs free energy and enthalpy.
  • Familiarity with the equation Delta H = Delta G + T * Delta S.
  • Knowledge of standard entropy values for gases at 298 K.
  • Basic stoichiometry related to chemical reactions and mole calculations.
NEXT STEPS
  • Study the derivation and applications of the Gibbs free energy equation.
  • Learn how to calculate standard entropy values for various substances.
  • Explore the concept of reaction stoichiometry in thermodynamic calculations.
  • Investigate the implications of Delta G and Delta H in chemical equilibrium.
USEFUL FOR

Chemistry students, educators, and professionals involved in thermodynamics and chemical reaction analysis will benefit from this discussion.

Coco12
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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?
 
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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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