Question

Consider the following reaction. K is .54 at 800 K. Calculate the equilibrium partial pressures of all species, starting with Pco2=1.00 atm; PH2= 1.00 atm Pco=Ph2O=0

CO2 (g) + H2 (g) ------CO (g) + H2O (g)

Answer 1

K could be either Kc or Kp, but let's confirm that with the following expression:_

Kp = Kc (RT)

= sum of coefficients of products - sum of coefficients of reactants

These coefficients are the numbers that balance the reaction. And in this reaction, all the compounds have 1 as coefficient (reaction already balanced)

= (1+1) - (1+1) = 0

Kp = Kc(RT)⁰

Kp = Kc

So after all, they are the same, so K is either Kc or Kp, but in these case, Kp is for pressures.

CO₂ + H₂ ------> CO + H₂O Kp = pCO * PH2O / PCO2 * PH2

i. 1 1 0 0

e. 1-x 1-x x x

0.54 = x² / (1-x)²

0.54(1-x)² = x²

0.54(1 - 2x + x²) = x²

0.54 - 1.08x + 0.54x² = x²

0.46x² + 1.08x - 0.54 = 0

x = -1.08 (1.08² + 4*0.46*0.54)^1/2 / 2*0.46

x = -1.08 (1.47) / 0.92

x₁ = 0.42 atm

x₂ = -2.77 atm

As X1 is positive, this would be the value of x that is the PCO and PH2O.

Hope this helps