## 2014 Midterm, #6 (pg.164)

$\ln K = -\frac{\Delta H^{\circ}}{RT} + \frac{\Delta S^{\circ}}{R}$

Yasmine Razi 3L
Posts: 4
Joined: Tue Nov 25, 2014 3:00 am

### 2014 Midterm, #6 (pg.164)

For question 6 in the 2014 midterm, when calculating -(delta)H/(RT) and (delta)S/R, why does the solution round these components, because I did it without rounding and my K has a great discrepancy between the answer (I got K=550760). So should we keep all the decimal places till the end, or should we round in the individual steps as well?
Also, for the same question, how should one do the significant figures when doing lnK=13.2, because Im a bit confused as to why the answer is given in 6 sigfigs?
Thanks!

Chem_Mod
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### Re: 2014 Midterm, #6 (pg.164)

I do not have that midterm in front of me, but to answer your question...

Sometimes, in the solutions to the midterms rounded values are used. However, if you use stored values and do not round until the end, your answer is actually more correct and you will not be docked any points. Also, you are correct in that you should not have 6 sig figs. They are just writing out the exact answer that they got. Usually when you see K values, they are just given in 2 or 3 sig figs. I would have to see how the exact problem is written with the other numerical values given in the question to see how sig figs are determined specifically for this question.

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

### Re: 2014 Midterm, #6 (pg.164)

Many of the problems that involve natural log have rounding errors. You'll be ok and you can always argue with your TA if you get it wrong.