Question

Consider the following reaction: 2CH4(g)⇌C2H2(g)+3H2(g) The reaction of CH4 is carried out at some temperature with an initial concentration of [CH4]=0.083M. At equilibrium, the concentration of H2 is 0.020 M . Find the equilibrium constant at this temperature. Express your answer using two significant figures.

Answer 1

         2CH4(g) <===>     C2H2(g)     + 3H2(g)

initial 0.083 M              0 M          0 M

change   0.02*2/3            0.02/3       0.02 M

         = 0.0133 M         = 0.0067 M

equil 0.083-0.0133          0.0067 M    0.02 M

        = 0.0697 M

   Kc = [C2H2][H2]^3/[CH4]^2

      = (0.02^3*0.0067)/(0.0697^2)

      = 1.1*10^-5