O THERMOCHEMISTRY 3/5 ARLY Understanding the definitions of heat and work A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1 atm. The cylinder is also submerged in a large insulated water bath. (See sketch at right.) 1 atm pressure piston cylinder The temperature of the water bath is monitored, and it is determined from this data that 185. kJ of heat flows out of the system during the reaction. The position of the piston is also monitored, and it is determined from this data that the piston does 357. kJ of work on the system during the reaction. water bath gases O exothermic Is the reaction exothermic or endothermic? O endothermic O up Does the temperature of the water bath go up or down? O down O neither O in Does the piston move in or out? O out O neither O absorb Does the reaction absorb or release energy? O release O neither How much energy does the reaction absorb or release? Be sure your answer has the correct number of significant digits.
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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