Nitrogen dioxide decomposes endothermically according to the balanced equation of A…

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

Nitrogen dioxide decomposes endothermically according to the balanced equation 2 NO2(g)→2 NO(g)+O2(g)ΔHrxn≈+114 kJ⋅mol−12\,\text{NO}_{2}(g) \rightarrow 2\,\text{NO}(g) + \text{O}_{2}(g) \quad \Delta H_{\text{rxn}} \approx +114\,\text{kJ}\cdot\text{mol}^{-1} of NO2\text{NO}_{2} A process engineer proposes coupling the decomposition with the exothermic reaction between hydrogen gas and oxygen gas so that the combined, single-step overall process becomes exothermic. 2 H2(g)+O2(g)→2 H2O(g)(bond energies to be used are listed below)2\,\text{H}_{2}(g) + \text{O}_{2}(g) \rightarrow 2\,\text{H}_{2}\text{O}(g) \quad (\text{bond energies to be used are listed below}) Average bond enthalpies (kJ⋅mol−1\text{kJ}\cdot\text{mol}^{-1}): N–O  201N=O  607O=O  498O–H  463H–H  436\text{N--O}\; 201 \quad \text{N=O}\; 607 \quad \text{O=O}\; 498 \quad \text{O--H}\; 463 \quad \text{H--H}\; 436 (a) Write a balanced chemical equation that combines an integer multiple of the NO2\text{NO}_{2} decomposition with an integer multiple of the H2/O2\text{H}_{2}/\text{O}_{2} reaction so that no elemental O2\text{O}_{2} appears in the overall products. (b) Using the bond enthalpy data, calculate ΔHrxn\Delta H_{\text{rxn}} for the overall process you derived in part (a). Show how bonds broken and formed are counted. (c) Determine whether the overall reaction you proposed is exothermic or endothermic. State the numerical value of ΔHrxn\Delta H_{\text{rxn}} with the correct sign and units.

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