Ethyl chloride (C₂H₂Cl) can be used as a topical anesthetic, for example prior to giving a painful injection. When liquid ethyl chloride is sprayed on the skin, energy absorbed from the skin causes the liquid to evaporate. This numbs the injection site by quickly decreasing the skin temperature to near o°C. How much heat (in kJ) is required to evaporate 2.84 mL of ethyl chloride at 25°C? kJ For C₂H₂Cl: d = 0.924 g/mL and AHº vap = 24.6 kJ/mol at 25°C.
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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