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Equilibrium Conversion. The gas-phase isomerization of o-xylene to the more stab

ID: 478799 • Letter: E

Question

Equilibrium Conversion. The gas-phase isomerization of o-xylene to the more stable p- xylene is occurring reversibly with an equilibrium constant based on concentration, K^C_eq in the pores of ZSM-5 (a type of zeolite catalyst). Typically, small molecules do not behave as ideal gases in the small pores of the zeolites where the isomerization reaction takes place, but for this analysis, you can assume that the isomers of toluene behave as ideal gases. Your co-worker at Exxon-Mobil measured the free energy of this reaction, delta G degree_rxn to be - 6 kJ mol^-1 and appeared independent of temperature over a 1000 K temperature range. At what temperature will the equilibrium conversion, X_eq for this isomerization reaction be equal to 0.8?

Explanation / Answer

we have relation betwene Xe ( equilibrium conversion) and Kc ( equilibrium constant)

Xe = Kc / ( 1+ Kc)

0.8 = Kc / ( 1+ Kc)

0.8 +0.8 Kc = Kc

Kc = 4

dGo = -RT ln K    is formula

where dGo = -6 KJ/mol = -6000 J/mol , R is gas constant

hence -6000 J/mol = - 8.314 J/molK   x T x ln ( 4)

T = 520.6 K

= 520.6 - 273.15 = 247.43 C

Thus at temp of 247.43 C we get Xeq = 0.8