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11.17

Posted: Mon Feb 05, 2018 10:55 am
by Lisa Tang 1C
For this problem, my answer was -2736.87 J, which is -2.7 kJ/mol when accounting for significant figures. The solution manual has -27 kJ/mol as the final answer. Is there something wrong with my math that is giving me the incorrect answer? My math looks exactly like what is shown in the manual.

Re: 11.17

Posted: Mon Feb 05, 2018 2:30 pm
by Chem_Mod
Please post what the problem is.

Re: 11.17

Posted: Mon Feb 05, 2018 2:49 pm
by Andrea ORiordan 1L
I'm not sure which problem you're referring to, but one thing to always double check is that your units for enthalpy and entropy are the same. Enthalpy is usually given in kJ, and entropy is usually given in J, which can sometimes lead to mistakes.

Re: 11.17

Posted: Mon Feb 05, 2018 5:07 pm
by April P 1C
I got -2.7kj/mol also. I think the solutions just had an error.

Re: 11.17

Posted: Mon Feb 05, 2018 5:54 pm
by Lisa Tang 1C
The problem is:
Calculate the reaction Gibbs free energy of N2(g) + 3H2(g)2NH3(g) when the partial pressures of N2,H2, and NH3 are 4.2 bar, 1.8 bar, and 21 bar, respectively. For this reaction, K=41 at 400. K.

I used the equation Gr=Gr(standard) + RTlnQ to solve and ended up with -2.7 kJ/mol.

Re: 11.17

Posted: Mon Feb 05, 2018 9:46 pm
by Kelly Kiremidjian 1C
I also got -2.74 kJ.mol-1. I think the there's a mistake in the answer key

Re: 11.17

Posted: Mon Feb 05, 2018 9:47 pm
by Sally Nason - 1K
I agree. I've put it in several different calculators and have gotten -2.7 kJ/mol every time.

Re: 11.17

Posted: Thu Feb 08, 2018 6:33 pm
by Wilson Yeh 1L
I also got -2.7 kJ/mol! I spent the past hour trying to figure out what I was doing wrong but it seems like it might just be an error in the solution.

Re: 11.17

Posted: Thu Feb 08, 2018 9:22 pm
by Alejandra Rios 1L
Your answer is correct, there are some typos in the solutions manual which can be found on Dr. Lavelle's website under course materials and titled solution manual errors. Here, Lavelle states, "11.17 Typo. The answer is -2.7 kJ.mol-1. (not -27 kJ.mol-1.,"

Re: 11.17

Posted: Thu Feb 08, 2018 11:03 pm
by Essly Mendoza 1J
Yes there is an error in the solutions manual and Dr.Lavelle has posted the correction on his website. The answer is -2.7 kj/mol.

Re: 11.17

Posted: Thu Feb 08, 2018 11:12 pm
by Christy Zhao 1H
Here is the link to the errors in the solution manual for future reference!
https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf