Homework Help: Chemistry

Posted by eliz on Sunday, March 1, 2009 at 5:48pm.

Question: Consider following equilibrium system: SO2(g)+ Cl2(g) goes to So2Cl2(g) Kp=.900 atm @25 degree C. Suppose that 2.0 moles S02, 1.0 moles Cl2, and 3.0 moles So2Cl2 are placed in an empty 4.00L vessel at 25 degree C. Compute teh number of grams of each substance present at equilibrium.

I set up an ICE table and converted all the moles of each substance to Molarity of each. Once i did that i got stuck, because the Kp is in atm and the other values are in molarity. What do i have to do to get atm of each and than convert those into grams?

Chemistry - DrBob222, Sunday, March 1, 2009 at 6:02pm
You can change Kp to Kc.
Chemistry - eliz, Sunday, March 1, 2009 at 6:06pm
How do you change Kp to Kc?
Chemistry - DrBob222, Sunday, March 1, 2009 at 7:42pm
Kc = Kp(RT)^-delta n where
delta n = n(gas products) - n(gas reactants)
Chemistry - eliz, Sunday, March 1, 2009 at 8:05pm
Please check my work?

I first changed Kp to Kc: .900atm(0.0821)(25+273.15)^(2.0 mol*1.0 mol)- (3.0)= 22.03

Than i did an ICE table. I than used the equation Kc= So2Cl2/So2*Cl2. 22.03=(.75+x)/(.5-x)(.25-x). I than solved for x. x=.169 was the only value that worked for x. I than substitued those into the each values to get moles than i changed them into grams of each. for the So2 I go 21.21g, for the Cl2 i got 5.74g and the SO2Cl2 i got 78.41 g. Is the correct way to do this problem?
Chemistry - DrBob222, Sunday, March 1, 2009 at 9:05pm
I didn't check the problem itself. I first checked the conversion of Kp to Kc.
First, you misunderstood the delta n part. The number of moles product n is 1 (its the coefficient, not the moles in the problem) and n for reactants is 2 (1+1)(again, not the values in the problem but the coefficients). Also, you turned it around; it should be products-reactants or 1-2=-1 BUT the good news is that your two errors canceled out and you came out with the right answer of -1. However, you did NOT include R within the parentheses so that makes your 22 incorrect.
I have Kc = Kp(RT)^-1 =
0.9/(0.08205*298.15) = about 0.04 but check my math. The 0.04 needs to be exact and not estimated on my part.

For the problem, you next need to determine which way the reaction is going in order to reach equilibrium.
SO2 + Cl2 ==> SO2Cl2
reaction quotient = (SO2Cl2)/(SO2)(Cl2) =
0.75/(0.5)(0.25) = 6.00
Since 6.00 is so much larger than 0.04, the reaction, as set up, is too far to the right so we know it will be shifting to the left.
Thus SO2 = 0.5+x; Cl2 = 0.25+x; SO2Cl2 = 0.75-x
and go from there.

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