Question

Find the temperature in ºC at which Kp = 43.7 for the reaction H2(g) + I2(g) ⇌ 2 HI(g). Use ∆Hºrxn and ∆Sºrxn to calculate and assume that they are independent of temperature. Use the thermodynamic data in the appendix of your textbook; I have provided the needed appendix on BlackBoard for your convenience. Report your answer to zero places past the decimal.

Answer 1

Go = - R T ln Kp

           = -8.314 x 10^-3 X 298 x ln 43.7

            = -9.36 kJ / mol

∆Hºrxn = ∆Hºproducts - ∆Hºreactant

           = 2 x 26.48 - (62.44 + 0)

          = -9.48 kJ / mol

∆Sºrxn = ∆Sºproducts - ∆Sºreactant

            = (2x206.5) - (260.6+130.6)

            = 21.8 J / K

           = 21.8 x 10^-3 kJ / K

Grxn = ∆Hºrxn - T ∆Sºrxn

-9.36 = -9.48 - T x 21.8 x 10^-3

T = -5.5 K

T = - 278.5 ^oC