Find equilibrium concentrations total pressure Please Help

Question

The reaction CO2(g)+C(s) reverse arrows 2CO(g)has kp=5.78at 1200K. Calculate the total pressure at equilibrium when 4.96g of CO2 is introduced into a 10.0 L container and heated to 1200 K in the presence of 3.71 g of graphite. Repeat the calculation with 0.45g of graphite. Answer to 3 significant figure.

I got 15.16 its wrong not sure what to do please help.

Thanks

Answer 1

First, we'll calculate the pressure of CO2 that is put into the container:

4.96 g CO₂ x 1 mol CO₂/44 g = 0.113 moles CO₂

PV = nRT and solve for P

P = nRT/V = (0.113 mol)(0.0821 Latm/Kmol)(1200K)/10.0 L

P = 1.11 atm

The moles of C(s) are not important because it is a solid and does not enter into the equilibrium expression.

Now we can set up an ICE table:

CO₂(g) + C(s) <==> 2CO(g)

1.11 atm...................0......I

-x..........-x...............+2x....C

1.11-x......................2x.....E

Kp = (CO)² / (CO₂)

5.78 = (2x)² / 1.11-x = 4x² / 1.11-x

4x² = 6.42 - 5.78x

4x² + 5.78x - 6.42 = 0

x = 0.736 atm

Pressure of CO = 2 x 0.736 atm = 1.47 atm

Pressure of CO₂ = 1.11 - 0.736 = 0.374 atm

Total pressure @ equilibrium = 1.47 atm + 0.374 atm = 1.84 atm