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

In summary, when gaseous nitrogen and hydrogen are converted to gaseous ammonia, the delta G value is -16.64Kj/mol. To calculate the delta h for the formation of ammonia using the given s values, the equation delta h = delta G + T delta s is used. The resulting value is 46.2 kj/mol, which is obtained by multiplying delta G by 2 and then dividing the sum by 2 moles. This is likely due to the data given being per mole of ammonia produced, rather than per mole of reaction. However, the data should be clearly stated to avoid ambiguity.
  • #1
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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  • #2
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.
 

1. What is the equation for calculating Delta G and Delta H for a chemical reaction?

The equation is: ΔG = ΔH - TΔS, where ΔG is the change in Gibbs free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

2. How do I determine the values for Delta G and Delta H in a chemical reaction?

You can determine the values for Delta G and Delta H by using standard enthalpy and entropy values for each molecule involved in the reaction. These values can be found in a reference table or calculated using thermodynamic equations.

3. What is the significance of calculating Delta G and Delta H for a chemical reaction?

Calculating Delta G and Delta H allows us to determine whether a reaction is spontaneous or non-spontaneous, as well as the direction and extent of the reaction. It also gives insight into the energy changes and thermodynamic stability of the reaction.

4. How does the stoichiometric coefficients affect the values for Delta G and Delta H?

The stoichiometric coefficients do not affect the values for Delta G and Delta H. These values are extensive properties, meaning they are independent of the amount of substance involved in the reaction.

5. Can Delta G or Delta H be negative?

Yes, both Delta G and Delta H can be negative. A negative Delta G indicates a spontaneous reaction, while a negative Delta H indicates an exothermic reaction. However, the magnitude of these values is important in determining the spontaneity and extent of the reaction.

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