Quick GC question

[drusier]

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hey guys im taking my DAT very soon and running though a 3 topscores in test conditions. Just finished the total science 1 and got all 18s (u think its reasonable to expect 20s on the real thing?) anyways my question si probabely easy but im fired right now:

14.25 moles of PCl5 gas in a 3.0L container comes to equilibrium at constant temp/pressure. 40% of the PCl5 decomposes according to:
PCl5(g)-->PCl3(g)+Cl2(g) what is the value of Kc for this reaction?

thanks in advance

(please work it out, so i can follow along)

oh one more thing on Bio1 a questioned asked:
all of the following are true of mitosis except :
and the right answer was : there is no crossing over of chromosomes
(i thouht there was only crossing over in meiosis?)

ps on the real dat do u get a timer like on topscore?

 

[ems5184]

Quoting jheidenr,

For Topscore exam I, #56....

Here are the essentials that you need to know:

Kc=[PCl3][Cl2]/[PCl5]

It says that there wre originally 14.25 moles of PCl5, but 40% decomposed. So 14.25*.4 = 5.7 moles. The remaining moles of PCl5 is now at (14.25-5.7) = 8.55 moles

Now you have the moles for each of the products and reactant, but you still have to convert them into concentrations (this is where I got hung up):

5.7 moles PCl3 / 3 liters = 1.9 M PCl3
5.7 moles Cl2 / 3 liters = 1.9 M Cl23
8.55 moles PCl3 / 3 liters = 2.85 M PCl3

So Kc=[PCl3][Cl2]/[PCl5] = [1.9]^2/2.85

First, try searching the forums to see if the question has been asked before, because most topscore ones have.

Hope this helps!

 

[drusier]

thx for the help, I was still wondering if you get a timer on the real DAT?

 

[podil]

thx for the help, I was still wondering if you get a timer on the real DAT?

All you get a countdown h:MM:SS from when the bio section begins to the end of the OChem section. Is this what u mean by timer? On the TopScore I never used their special timing option (I forgot what its called).

 

[drusier]

cool thats all i need

 

[phosphorylation]

hey guys im taking my DAT very soon and running though a 3 topscores in test conditions. Just finished the total science 1 and got all 18s (u think its reasonable to expect 20s on the real thing?) anyways my question si probabely easy but im fired right now:

14.25 moles of PCl5 gas in a 3.0L container comes to equilibrium at constant temp/pressure. 40% of the PCl5 decomposes according to:
PCl5(g)-->PCl3(g)+Cl2(g) what is the value of Kc for this reaction?

thanks in advance

(please work it out, so i can follow along)

oh one more thing on Bio1 a questioned asked:
all of the following are true of mitosis except :
and the right answer was : there is no crossing over of chromosomes
(i thouht there was only crossing over in meiosis?)

ps on the real dat do u get a timer like on topscore?

im confused about your bio question. i also thought there was no crossing over in mitosis, only meiosis...

 

[podil]

That must be a typo for meiosis.

I believe chromosomes dont pair during mitosis. Pairing is necessary for crosing over, which occurs in Meiosis Prophase I.

-P