A researcher wishes to determine the enthalpy change for the industrial synthesis of…

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

Problem

A researcher wishes to determine the enthalpy change for the industrial synthesis of nitric acid represented by the overall process 4 NO2(g)+O2(g)+2 H2O(l)→4 HNO3(aq)4\,\text{NO}_2(g) + \text{O}_2(g) + 2\,H_2\text{O}(l) \rightarrow 4\,\text{HNO}_3(aq) A junior technician combined the following three reactions in the order shown and claimed the resulting ΔH\Delta H is −314 kJ-314\,\text{kJ}. All numerical values given for the individual reactions are thermodynamically correct. (1) 2 NO2(g)+O2(g)→2 NO3(g)2\,\text{NO}_2(g) + \text{O}_2(g) \rightarrow 2\,\text{NO}_3(g)  ΔH=−56 kJ\Delta H = -56\,\text{kJ} (2) NO3(g)+H2O(l)→HNO3(aq)\text{NO}_3(g) + H_2\text{O}(l) \rightarrow \text{HNO}_3(aq)  ΔH=−169 kJ\Delta H = -169\,\text{kJ} (3) NO3(g)→NO2(g)+12 O2(g)\text{NO}_3(g) \rightarrow \text{NO}_2(g) + \frac{1}{2}\,\text{O}_2(g)  ΔH=+88 kJ\Delta H = +88\,\text{kJ} The technician doubled reaction (1) and reaction (2) and then added reaction (3) four times before summing the ΔH\Delta H values. The notebook page shows the final net equation as identical to the target process. (a) Verify whether the technician’s written net equation actually matches the target equation by performing a systematic species and coefficient check. List any discrepancies you find. (b) Determine which reactions must be reversed or multiplied by alternative factors so that, after combination, all intermediate species (including NO3(g)\text{NO}_3(g)) are eliminated and the stoichiometry of every remaining species aligns with the target process. Provide your corrected set of transformed reactions. (c) Using the corrected set from part (b), recompute ΔH\Delta H for the overall synthesis of nitric acid. Express your answer to three significant figures with the proper unit. (d) The technician asserted that because NO3(g)\text{NO}_3(g) appears on both sides of the summed equation, its enthalpy contribution cancels automatically regardless of coefficient mismatch. Evaluate this claim with a quantitative example drawn from your calculations in part (c).

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