Answer
38.8 kJ/mol
Work Step by Step
$\ln \frac{K_{2}}{K_{1}}=-\frac{\Delta H^{\circ}_{rxn}}{R}(\frac{1}{T_{2}}-\frac{1}{T_{1}})$
$\implies \ln\frac{8.5\times10^{3}}{0.65}=-\frac{\Delta H^{\circ}_{rxn}}{8.314\,Jmol^{-1}K^{-1}}(\frac{1}{755\,K}-\frac{1}{298\,K})$
$\implies 9.4786=-\frac{\Delta H^{\circ}_{rxn}}{8.314\,Jmol^{-1}K^{-1}}\times-0.0020312\,K$
$\implies \Delta H^{\circ}_{rxn}=\frac{9.4786\times8.314\,J/mol}{0.0020312}=38800\,J/mol$
$=38.8\,kJ/mol$
