A research group measures the standard enthalpy change for the following reaction at…

CHEMISTRY · Multi-part · AP · Chemistry · Thermochemistry · Thermochemistry

Problem

A research group measures the standard enthalpy change for the following reaction at 298 K298\,\text{K} and 1 atm1\,\text{atm} to be −371 kJ mol−1-371\,\text{kJ mol}^{-1} per mole of reaction: NH3(g)+2 O2(g)→HNO3(l)+H2O(l)NH_3(g) + 2\,O_2(g) \rightarrow HNO_3(l) + H_2O(l) Standard enthalpies of formation, ΔHf∘\Delta H_f^\circ (kJ mol−1\text{kJ mol}^{-1}): • NH3(g)NH_3(g) = −46.1-46.1  • H2O(l)H_2O(l) = −285.8-285.8  • O2(g)O_2(g) = 0.00.0 The ΔHf∘\Delta H_f^\circ of HNO3(l)HNO_3(l) is not tabulated in the reference used by the group. (a) Determine the standard enthalpy of formation, ΔHf∘\Delta H_f^\circ, of HNO3(l)HNO_3(l) using the measured reaction enthalpy and the data provided. Show each step of your reasoning. (b) Explain what the sign and magnitude of your calculated ΔHf∘\Delta H_f^\circ imply about the relative stability of HNO3(l)HNO_3(l) with respect to its constituent elements. (c) Classify the reaction as exothermic or endothermic and support your classification quantitatively.

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