We can use Hess's Law (and some creativity!) to learn about the energetics of reactions that occur in remote environments. Consider the atmospheric reaction, NO + O → NO₂ (a) Use the dissociation energy of O2, 498.34 kJ/mol, and the standard heats of formation for NO (+90.25 kJ/mol) and NO₂ (+33.18 kJ/mol) to derive the enthalpy change for this reaction. QUESTION 14 (b) The two bonds in NO2 are equivalent, and we can use the bond strength of N₂, 945 kJ/mol, and the information given in part (a) to determine ArxnH for N+O+O→ NO₂ From this ArxnH, estimate the bond strength of each of the resulting N-O bonds in kJ/mol. (Note: Your answer for this part does not necessarily depend on your answer to part a).
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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