Homework 8.59

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Tyler Miao 1A
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Joined: Wed Sep 21, 2016 2:59 pm

Homework 8.59

Postby Tyler Miao 1A » Mon Jan 16, 2017 12:55 pm

For 8.59, it says to calculate standard reaction enthalpy, so when I am trying to products - reactants, why does the solution manual leave out 7mols of N2? In the notes, it includes everything, regardless of state of matter?

isabelle ruedisueli 1j
Posts: 21
Joined: Wed Sep 21, 2016 2:56 pm

Postby isabelle ruedisueli 1j » Mon Jan 16, 2017 3:25 pm

Hi. In Appendix 2a it shows that the enthalpy of formation for N2 is actually 0, so it doesn't need to be included in the equation. Hope this helps!

Michelle_Li_1H
Posts: 32
Joined: Wed Sep 21, 2016 3:00 pm

Re: Homework 8.59

Postby Michelle_Li_1H » Mon Jan 16, 2017 3:31 pm

You are correct by calculating the standard enthalpy of formation of the products and subtracting the standard enthalpy of formation of the reactants. However, as we went over in class, the standard enthalpy of formation of an element in its most stable form is zero.

In this case, the most stable form of N is the gas state of N2. To answer your question, the equation includes the 7 mols of N2 but it isn't written out because you would simply be adding 0.

Hope this helps!


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