Question

From information in the “Data section” of your textbook, calculate the standard

Gibbs free energy and the equilibrium constant at (a) 25°C and (b) 50°C for the reaction

CH4(g) + 3 Cl2(g) <--> CHCl3(l) + 3 HCl (g).

Assume that the reactionenthalpy isindependent of temperature.

ΔG°f (CHCl3, l) =-­71.8 kJ/mol, ΔH°f(CHCl3, l) =‐132.2 kJ/mol

Which extra DATA can i provide from the textbook. What values should I look for?

Answer 1

For the given reaction,

dGo at (a) 25 oC + 273 = 298 K

dGo = dGo(products) - dGo(reactants)

        = (-71.8 + 3 x -95.31) - (-50.84 + 3 x 0)

        = -306.9 kJ/mol

dGo = -RTlnK

equilibrium constant (K)

-306.9 x 10^3 J/mol = - 8.314 x 298 lnK

K = 6.26 x 10^53

(b) at T = 50 oC + 273 = 323 K

dHo = dHo(products) - dHo(reactants)

        = (-132.2 + 3 x -92.30) - (-75 + 3 x 0)

        = -334.1 kJ/mol

dSo = dSo(products) - dSo(reactants)

        = (201.7 + 3 x 187) - (186.3 + 3 x 223)

        = -92.6 J/K.mol

dGo = dHo - TdSo

        = -334.1 - 323 x -0.0926

        = -304.2 kJ/mol

dGo = -RTlnK

equilibrium constant (K)

-304.2 x 10^3 J/mol = - 8.314 x 323 lnK

K = 1.57 x 10^49

check the values of standard dHo, dSo and dGo and reconfirm your results.