Help with finding Kp

Question

Carbon disulfide is a foul smelling solvent that dissolves sulfur and other nonpolar substances. It can be made by heating sulfur in an atmosphere of methane.

4CH4 (g) + S8 (s) ⇔ 4CS2 (g) + 8H2 (g)

Starting with the following data, calculate the values of Kp for the reaction at 25 °C and 500 °C. ∆𝐻f° = 115.3 kJ/mol, ΔS°= 237.8 kJ/mol ⋅ K, and ∆𝐺f° = 65.1 kJ/mol.

Answer 1

Two equations you need to know are:

 

dG = R T ln(Kp)

 

dG= dH-TdS

 

At standard conditions (25C, 1 atm), we are told dG= 65.1 kJ/mol

dG = R T ln(Kp)

65100=(8.314)(273+25)(ln(Kp))

∴Kp =2.58x10¹¹ atm⁷

NB: this Kp looks very large.