• # question_answer 25) Enthalpies of formation of $CO(g),C{{O}_{2}}(g),{{N}_{2}}O(g)$and${{N}_{2}}{{O}_{4}}(g)$ are$-110,-393,+81$and$+9.7kJ\,mo{{l}^{-1}}$respectively. Find the value of${{\Delta }_{r}}H$ for the reaction:

Information shadow: The reaction is: ${{N}_{2}}{{O}_{4}}(g)+3CO(g)\to {{N}_{2}}O(g)+3C{{O}_{2}}(g)$ ${{\Delta }_{f}}H_{Co(g)}^{{}^\circ }=-110kJ\,mo{{l}^{-1}}$ ${{\Delta }_{f}}H_{C{{O}_{2}}}^{{}^\circ }=-393kJmo{{l}^{-1}}$ ${{\Delta }_{f}}H_{{{N}_{2}}O(g)}^{{}^\circ }=+81kJ\,mo{{l}^{-1}}$ ${{\Delta }_{f}}H_{{{N}_{2}}{{O}_{4}}(g)}^{{}^\circ }=+9.7kJ\,mo{{l}^{-1}}$ Problem solving strategy: ${{\Delta }_{r}}{{H}^{{}^\circ }}=\Sigma {{\Delta }_{f}}H_{\text{Products}}^{{}^\circ }-\Sigma {{\Delta }_{f}}H_{\text{Reactants}}^{{}^\circ }$ Working it out: ${{\Delta }_{r}}{{H}^{{}^\circ }}=[{{\Delta }_{f}}H_{{{N}_{2}}O(g)}^{{}^\circ }+3{{\Delta }_{f}}H_{C{{O}_{2}}(g)}^{{}^\circ }]$ $-[{{\Delta }_{f}}H_{{{N}_{2}}{{O}_{4}}(g)}^{{}^\circ }+3{{\Delta }_{f}}H_{CO(g)}^{{}^\circ }]$ $=[81+3(-393)]-[9.7+3(-110)]=-777.7kJ$