91Ó°ÊÓ

To calculate the enthalpy change for each reaction, we will use the equation: \[ \Delta H^{\circ}_{reaction} = \sum \Delta H^{\circ}_{f,\,products} - \sum \Delta H^{\circ}_{f,\,reactants} \] For each reaction, we will find the enthalpy change using the enthalpy of formation values provided in Appendix 4. Reaction 1: \(4 NH_3(g) + 5 O_2(g) \rightarrow 4 NO(g) + 6 H_2O(g)\) \[ \begin{aligned} \Delta H^{\circ}_{1} &= [4 \times \Delta H^{\circ}_{f,\,NO(g)} + 6 \times \Delta H^{\circ}_{f,\,H_{2}O(g)}] - [4 \times \Delta H^{\circ}_{f,\,NH_{3}(g)}]\\ \end{aligned} \] Reaction 2: \(2 NO(g) + O_2(g) \rightarrow 2 NO_2(g)\) \[ \begin{aligned} \Delta H^{\circ}_{2} &= [2 \times \Delta H^{\circ}_{f,\,NO_{2}(g)}] - [2 \times \Delta H^{\circ}_{f,\,NO(g)}]\\ \end{aligned} \] Reaction 3: \(3 NO_2(g) + H_2O(l) \rightarrow 2 HNO_3(aq) + NO(g)\) \[ \begin{aligned} \Delta H^{\circ}_{3} &= [2 \times \Delta H^{\circ}_{f,\,HNO_{3}(aq)} + \Delta H^{\circ}_{f,\,NO(g)}] - [3 \times \Delta H^{\circ}_{f,\,NO_{2}(g)} + \Delta H^{\circ}_{f,\,H_{2}O(l)}]\\ \end{aligned} \] Now, plug in the enthalpy of formation values from Appendix 4 and calculate the values of \(\Delta H^\circ_{1}\), \(\Delta H^\circ_{2}\) and \(\Delta H^\circ_{3}\).

In order to find the overall equation for the Ostwald process, we will add the three reactions together and eliminate any substance that appears on both sides of the equation. Reaction 1: \(4 NH_3(g) + 5 O_2(g) \rightarrow 4 NO(g) + 6 H_2O(g)\) Reaction 2: \(2 NO(g) + O_2(g) \rightarrow 2 NO_2(g)\) Reaction 3: \(3 NO_2(g) + H_2O(l) \rightarrow 2 HNO_3(aq) + NO(g)\) Overall Equation: \(4 NH_3(g) + 5 O_2(g) \rightarrow 2 HNO_3(aq) + 3 H_2O(g) + H_2O(l)\) To determine whether the overall reaction is exothermic or endothermic, we will check the sum of the enthalpy changes of the individual reactions: \[ \Delta H^\circ_{overall} = \Delta H^{\circ}_{1} + \Delta H^{\circ}_{2} + \Delta H^{\circ}_{3} \] If \(\Delta H^\circ_{overall} < 0\), the overall reaction is exothermic. If \(\Delta H^\circ_{overall} > 0\), the overall reaction is endothermic. Calculate \(\Delta H^\circ_{overall}\) using the previously calculated values of \(\Delta H^\circ_{1}\), \(\Delta H^\circ_{2}\) and \(\Delta H^\circ_{3}\), and determine whether the reaction is exothermic or endothermic.