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ratio of product / reactant

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ratio of product / reactant

Postby Tiamaria » Thu Jan 20, 2011 7:24 pm

Hello Everyone.
I'm stuck on a few questions. But since they are long, I will post one at a time. I'm just working on a study workbook that was recommended for my biology class, but i can only get half way done the problems. I hope you can help.

1. For the reaction:

dihydroxyacetone phosphate <----> glyceraldehyde 3-phosphate
Delta G' = 1.8kcal/mol (I'll use this symbol ^ for delta)

What ratio of product/reactant must be maintained in order to keep the rxn going in a forward direction?

So this is what I've got so far ( and the back of the book shows the answer, but it doesnt show all the steps so it loses me near the end)

^G' < 0
^G' + 2.303 RT Log (glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < 0
1.8 kcal = 1800 cal

1800 cal/mol + (2.303) (1.987cal/mol K) (298K) log (glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < 0

1364 Log (glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < -1800cal/mol

Log (glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < -1800 / 1364

Log (glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < -1.32cal/mol

Then from here I dont know how to get rid of "log"

The final answer says it should be

(glyceraldehyde 3-phosphate) / (dihydroxyacetone phoshate) < 0.048 cal/mol

How did it go from -1.32 cal to 0.048 cal

Please help.
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Postby JackBean » Thu Jan 20, 2011 7:30 pm

LOL, that's all what you need? Just convert logarithm to normal number?

log (10^x) = x
^ here means power, so you can have like:
log 100 = log (10^2) = 2
pretty simple, isn't it?

(of course, this is decimal logarithm, but the basis can be any)

Cis or trans? That's what matters.
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Postby Tiamaria » Thu Jan 20, 2011 7:38 pm

i still dont understand. can you break it down step by step for me.. i know i'm slow with this :(

how does that -1.32 get to be .048?
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Postby canalon » Thu Jan 20, 2011 11:52 pm

Log is a logarithm:
explanation in wikipedia:
basic maths skills are useful in biology, you know?

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)
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