Question

A mixture of water and graphite is heated to 600 K. When the system comes to equilibrium it contains 0.13 mol of H₂, 0.13 mol of CO, 0.43 mol of H₂O, and some graphite. Some O₂ is added to the system and a spark is applied so that the H₂ reacts completely with the O₂.

Find the amount of CO in the flask when the system returns to equilibrium.
Express your answer to two significant figures and include the appropriate units.

Answer 1

C(s) + H2O(g) ----------. CO (g) + H2(g)

   Kc   = [CO][H2]/[H2O]

           = 0.13*0.13/0.43   = 0.0393

    H2(g) + 1/2O2 (g) ------------------. H2O (g)

1 mole of H2 react with O2 to gives 1 mole of H2O

0.13 moles of H2 react with O2 to gives 0.13 moles of H2O

   [H2O]   = 0.43+ 0.13 = 0.56M

         C(s) + H2O(g) ----------. CO (g) + H2(g)

I                    0.56 0.13    0

C                     -x                        +x         +x

E                   0.56-x                0.13+x      +x

        Kc = [CO][H2]/[H2O]

      0.0393 = (0.13+x)*x/(0.56-x)

    0.0393*(0.56-x) = (0.13+x)*x

         x = 0.086

   [H2]   = x   = 0.086M

[CO]   = 0.13+x   = 0.13+0.086   = 0.216M

[H2O]   = 0.56-x   = 0.56-0.086   = 0.474M

    Kc   = [CO][H2]/[H2O]

           = 0.216*0.086/0.474   = 0.0393

It is correct solution