Answer
480 kJ/mol
Work Step by Step
$\Delta n=\text{number of moles of product gases}-\text{number of moles of reactant gas}$
$=3-2=1$
$\Delta U= \Delta H-\Delta(nRT)$
$=\Delta H-RT\Delta n$
$=483.6\times10^{3}\,J/mol-(8.314\,J\,mol^{-1}K^{-1})(273+125)K\times(1)=4.80\times10^{5}\,J/mol$
$=480\,kJ/mol$
