## Winter 2016 Final Exam Q2A [ENDORSED]

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Absolute Zero 1O
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Joined: Wed Sep 21, 2016 2:56 pm

### Winter 2016 Final Exam Q2A

Just a quick question, are partial pressures always supposed to be in bars? Once we have K=2x/x^2, how did we know that the unit for x would be bar, and not atm for example?

Claudette_Contr_3I
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### Re: Winter 2016 Final Exam Q2A

I think this is because bar may be the standard unit for partial pressures. Whether you need the partial pressure in bar or in atm form relies on the question.

Stephanie Demo 2N
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Joined: Thu Sep 29, 2016 3:00 am

### Re: Winter 2016 Final Exam Q2A

Last quarter in 14A, Professor Li said that it is common practice to use bar as the unit of pressure, but I'm not sure if Dr. Lavelle specified using bar or atm. Just be sure that you are consistent with units when doing calculations so that you don't lose points for conversions.

Aliya Habib 1L
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### Re: Winter 2016 Final Exam Q2A

I think you just work with the units you are given in the question.

Raul Hernandez
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### Re: Winter 2016 Final Exam Q2A

Kind of unrelated question but: why is it 2X on the top? I didn't quite get that in the review session. Do you mind explaining that part?

Jennifer Ngo 1M
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Joined: Sat Jul 09, 2016 3:00 am

### Re: Winter 2016 Final Exam Q2A

Raul Hernandez wrote:Kind of unrelated question but: why is it 2X on the top? I didn't quite get that in the review session. Do you mind explaining that part?

The reactants are half of the products aka the products are double the reactants. He made the concentration of the reactants "x," so products would be "2x." You also could have made the products "x" and reactants "x/2"

Chem_Mod
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### Re: Winter 2016 Final Exam Q2A  [ENDORSED]

Bar is the SI unit for pressure (and very close to ATM).

The question stated, "Calculate the partial pressures in bar."

1.00 atm = 1.01 bar Very similar, which is why we often use atm even though bar is the official SI unit for pressure (as I mentioned several times in Chem 14A and in my 2 hour review today.

This was discussed in detail in my review.

Kiara1F
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Joined: Fri Sep 25, 2015 3:00 am

### Re: Winter 2016 Final Exam Q2A

why is there an x^2 on the bottom?
Is it because there are 2 reactants?
It just threw me off because I was thinking in terms of only squaring the number if they had coefficients in front of them but they don't. But there are 2 sets of reactants....