Given the standard reactions N2 + 2O2 ⇌ 2NO2 (ΔG° = 100 kJ/mole) and NO + ½O2 ⇌ 2NO2 (ΔG° = -35 kJ/mole), what is the standard free energy of formation of NO in kJ/mole___________________?
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Answer: C. 85
Explanation
Standard free energy changes of chemical reactions can be combined using thermodynamic cycles and Hess law. Subtracting or adding reaction equations allows calculation of the standard free energy of formation for nitric oxide. Performing the correct stoichiometric combination yields a standard free energy of formation equal to eighty five. Standard free energy of formation is the free energy change accompanying formation of a compound from elements. Hess law states that total enthalpy or free energy change is independent of the reaction pathway taken. Equilibrium constants are directly related to standard Gibbs free energy changes through thermodynamic equations.
Chemical plant designers use formation free energies to predict equilibrium yields for high temperature reactions. Combustion emission analyses track nitrogen oxide formation mechanisms inside industrial furnaces and engines. Thermodynamic databases rely on consistent free energy calculations for evaluating novel industrial processes. Fifteen is an incorrect calculation result derived from improper combination of reaction free energy values. Thirty is an inaccurate numerical value resulting from arithmetic errors during thermodynamic cycle balancing. One hundred and seventy overestimates the free energy change by failing to balance stoichiometric coefficients.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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