Homework Help: chem

Posted by Hannah on Wednesday, February 20, 2013 at 4:57pm.

(a) At 800 K the equilibrium constant for I2(g) 2 I(g) is Kc = 3.1 10-5. If an equilibrium mixture in a 10.0-L vessel contains 3.25 10-2 g of I(g), how many grams of I2 are in the mixture?

(b) For 2 SO2(g) + O2(g) 2 SO3(g), Kp = 3.0 104 at 700 K. In a 2.00-L vessel the equilibrium mixture contains 1.46 g of SO3 and 0.130 g of O2. How many grams of SO2 are in the vessel?

how do you do these?

chem - DrBob222, Wednesday, February 20, 2013 at 5:58pm
3.25E-2/10L = 2.56E-4 mol and
2.56E-4/10 = 2.56E-5 M

........I2 ==> 2I
E.......?......2.56E-5M

Kc = (I)^2/(I2)
You know Kc and I, solve for I2 in molarity, then convert to grams in the 10 L container.

1.46/80 = about 0.01825 mols SO3.
0.130/32 = about 0.0041 mols O2.

............2SO2 + O2 ==> 2SO3
Why can't you use PV = nRT to solve for pSO2 and again for pO2. Substitute these numbers in Kp expression and solve for pSO2. Finally, use PV = nRT and convert pSO2 to n and to grams. Post your work if you get stuck.
chem - Devron, Wednesday, February 20, 2013 at 6:10pm
A.)
You have to convert the concentrations to molarity

3.25 x10^-2 g/126.9g*mol-1=moles of I

moles of I/10L=molarity

I2(g)---->2I(g)

I2=[x]
2I=(moles of I2/10L)^2

Since Kc =3.1 x10^-5=products/reactants,

Kc=3.1 x10^-5=(moles of 2I/10L)^2/[x]

Solve for x

to get grams of I2,

Molarity*10L=moles of I2

moles of I2*253.8g*mol-1= g of I2

B.)
2SO2(g)----> O2(g) + 2SO3(g)

You have to convert everything to molarity. I showed you how to do this in A, and you have to find the molecular weights of the compounds in question.

Kp = 3.0 x 10^4 =products/reactants=(SO3)^2(O2)/[2x]^2

solve for x

Multiply x by 2 to get molarity of SO2 and use the same setup that I gave you in A to get grams of SO2
chem - Devron, Wednesday, February 20, 2013 at 6:11pm
Didn't know that you were answering it.
chem - DrBob222, Wednesday, February 20, 2013 at 6:44pm
Note that in a you must convert to M as I did.
Note that in b you do not need to convert to M because part b is Kp and not Kc. Pressure is what you want in part b and molarity won't do it unless you wish to use molarity to find pressure.
chem - Devron, Wednesday, February 20, 2013 at 6:55pm
Kp=is pressure, I apologize about that one. So, you have to use the setup that DrBob222 gave you in his initial post.

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