Consider the molecules of furan and benzene. The dominant Lewis structure of furan and the two resonance structures of benzene are shown below: Furan H H H K Xxx What is the meaning of the double-sided arrow () connecting the two structures of benzene? Benzene H H H H It indicates that electrons in benzene rapidly change their positions corresponding to the two structures. It indicates that there are two independent coexisting forms of benzene. It indicates a chemical equilibrium between the two distinct structures. It indicates that the second structure can be obtained as a mirror image of the first one. It indicates that benzene exists in a single form, which is an average of the two structures.
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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