Question

The toxic (and energetically inefficient) carbon monoxide produced during combustion can be turned into hydrogen fuel in the water-gas shift reaction shown below. If the reaction is already at equilibrium with CO, water, and hydrogen concentrations all equaling 0.10 M and the carbon dioxide concentration at 0.40 M, and an extra 0.60 mol of carbon dioxide is now added to the 2.0 L reaction vessel, what will be the new hydrogen concentration once equilibrium is reestablished?

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

Answer 1

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

0.1          0.1                0.40         0.1

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

     = 0.4 x 0.1 / 0.1^2

    = 4

concentration of CO2 = 0.6 / 2 = 0.30 M

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

0.1          0.1                0.4             0.1

0.1         0.1                  0.7             0.1

0.1+x     0.1+x               0.7-x         0.1-x

Kc = (0.7-x)(0.1 - x) / (0.1+x)^2

4 = x^2 - 0.8x + 0.07 / (0.1+x)^2

x = 0.0181

new hydrogen concentration = 0.1 - 0.0181

new hydrogen concentration = 0.082 M