J. W. Hill, R. H. Petrucci, T. W. McCreary, & S. S. Perry General Chemistry 4th edition

Problem 17.62

The following reaction is carried out on an industrial scale for the production of thionyl chloride, a chemical used in the manufacture of pesticides.

SO3(g) + SCl2(l)OSCl2(l) + SO2(g)

The thermodynamic data listed below are for 298 K. Use these data and data from Appendix C to determine the temperature at which Keq = 1.0×1015 for the reaction.
 Hof, kJ/mol So, Jmol–1K–1 SCl2(l) –50.0 184 OSCl2(l) –245.6 121

First, find Go from Hof and So data. Then use Go = –RTlnKeq = Ho – TSo to find the required temperature.

Hof(SO2(g)) = –296.8 kJ/mol
Hof(SO3(g)) = –395.7 kJ/mol
Hof(SCl2(g)) = –50.0 kJ/mol
Hof(OSCl2(g)) = –245.6 kJ/mol

Ho = [–245.6 + –296.8] – [–395.7 + –50.0] = –96.7 kJ

So(SO2(g)) = 248.1 J/mol•K
Sof(SO3(g)) = 256.6 J/mol•K
Sof(SCl2(g)) = 184 J/mol•K
Sof(OSCl2(g)) = 121 J/mol•K

So = [121 + 248.1] – [256.6 + 184] = –72 J/K

–(8.314)Tln(1.0×1015) = –96700 – T(–72)
–287T = –96700 + 72T
–359T = –96700
T = 269 K (= –4 oC)