[Navystreak]

Hey, I haven't had much luck with physical chemistry for a while, was hoping for some help with a few questions to get my revision started...

1.

Consider the dissociation of Iodine:
I2(g) <-> 2I(g)
A 1.00g sample of I2 is heated at 1200C in a 500mL flask. At equilibrium the total pressure is 1.51atm. Calculate the equilibrium constant for the reaction.

So far I've written that Kp = PI^2 / PI2 and pV=nRT but I'm not too sure where to go from here?



2.

The equilibrium constant for the reaction
H2(g) + CO2(g) <-> H2O(g) + CO(g)
is 4.1 at 1650C. Initially 0.8mol of H2 and 0.8mol of CO2 are injected into a 5.0L flask. Calculate the concentration of each species at equilibrium.


Now here I've this written out:

H2 CO2 H2O CO
Initial 0.8 0.8 0 0
EQ


and also Kc = [H2O][CO] / [H2][CO2]


any help is appreciated!

[Navystreak]

I believe I may have answered my own question 1.

if pV=nRT, p = 0.95atm

I2 2I
initial 0.95 0
equilibrium 0.95-x 2x

PI2 + PI = 0.95-x+2x=1.51

x = 0.557

Kp = 2x^2 / 0.95-x = 3.13

Verification?

[shengoc]

Originally Posted by Navystreak

I believe I may have answered my own question 1.

if pV=nRT, p = 0.95atm

I2 2I
initial 0.95 0
equilibrium 0.95-x 2x

PI2 + PI = 0.95-x+2x=1.51

x = 0.557

Kp = 2x^2 / 0.95-x = 3.13

Verification?

You can't assume I2 is a perfect gas, can you? and i think just using
partial pressure = mole fraction x total pressure should suffice for the Kp eqn. not too sure though.

[shengoc]

2. The equilibrium constant for the reaction
H2(g) + CO2(g) <-> H2O(g) + CO(g)
is 4.1 at 1650C. Initially 0.8mol of H2 and 0.8mol of CO2 are injected into a 5.0L flask. Calculate the concentration of each species at equilibrium.


Now here I've this written out:

H2 CO2 H2O CO
Initial 0.8 0.8 0 0
EQ


and also Kc = [H2O][CO] / [H2][CO2]


any help is appreciated![/quote]

Suppose x mole of H2 dissociated already at eqm, then mole of H2 = mole of CO2 = 0.8 - x
and mole of H2O and mole of CO equal to x

Total mole = 1.6
Total pressure = P
Kp = 4.1(all are gases, so it must be Kp instead of Kc)

Partial pressure = mole fraction x total pressure
ie, partial pressure of H2 at eqm = (0.8-x)/1.6 x P

But the P will cancel out,so does the 1.6, what i get is x = 0.8/(root of 4.1 + 1)

then from no.of mole, and you know the volume of the container, i guess to find Kc, you need concentration, so it is just mole/volume in dm^3 and then do the Kc calculation.