A sample of pure solid naphthalene (C10H8) weighing 0.6410 g is burned completely with oxygen to CO2(g) and H2O(,) in a constant-volume calorimeter at 25°C. The amount of heat evolved is observed to be 25.79 kJ. (a) Write and balance the chemical equation for the combustion reaction. (b) Calculate the standard change in internal energy (DU°) for the combustion of 1.000 mol naphthalene to CO2(g) and H2O(,). (c) Calculate the standard enthalpy change (DH°) for the same reaction as in part (b).
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.
A sample of pure solid naphthalene (C10H8) weighing 0.6410 g is burned completely with oxygen to CO2(g) and H2O(,) in a constant-volume calorimeter at 25°C. The amount of heat evolved is observed to be 25.79 kJ.
(a) Write and balance the chemical equation for the combustion reaction.
(b) Calculate the standard change in internal energy (DU°) for the combustion of 1.000 mol naphthalene to CO2(g) and H2O(,).
(c) Calculate the standard enthalpy change (DH°) for the same reaction as in part (b).
(d) Calculate the standard enthalpy of formation per mole of naphthalene, using data for the standard enthalpies of formation of CO2(g) and H2O(,) from Appendix D.
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