# Homework Help: Free energy question involving Kp and deltaG

1. Dec 1, 2012

### hahaha158

1. The problem statement, all variables and given/known data

The following reaction takes place at standard conditions

4NH3(g)+6NO(g)----->5N2(g)+6H20

A)calculate reaction enthalpy and Gibbs reaction energy

B)Calculate Kp

2. Relevant equations

the table gives the following values for deltaG0f[X]
NH3(g)=-16.5 Kj/mol
NO(g)=87.6 KJ/mol
H20(g)=-228.6 KJ/mol

ln(Kp)=-deltaG/(RT)

3. The attempt at a solution

I finished part a) and found gibbs reaction energy to be -1815 KJ

For part b) i am unsure of what to enter for deltaG in the equation ln(Kp)=-deltaG/(RT). Do I use the reaction energy calculated from part a), deltaG for NH3, NO, or H20? Any help is appreciated, thanks!

2. Apr 20, 2015

### kaja

you would use the standard DG found by this formula:
∑nΔGoproducts - ΣmΔGoreactants

3. Apr 20, 2015

### kaja

-the n and m being the coefficients for each molecule

4. Apr 20, 2015

### Staff: Mentor

You use the ΔG0 that you calculated in part a (I didn't check your arithmetic). (Also, that should not be a ΔG in the equation; it should be ΔG0). To get the standard reaction enthalpy, you need to know the standard heats of formation. Did they give you these?

Chet