When a 2.000-gram sample of pure phenol, C6H5OH(s), is completely burned according to the equation above, 64.98 kilojoules of heat is released. Use the information in the table below to answer the questions that follow. Standard Heat of Substance Formation, AHᵒf, at 25°C (kJ/mol) C(graphite) CO₂(g) H₂(g) H₂O(1) O₂(g) C6H5OH(s) 0.00 -395.5 0.00 -285.85 0.00 ? Absolute Entropy, So, at 25°C (J/mol-K) 5.69 213.6 130.6 69.91 205.0 144.0 (a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25°C. (b) Calculate the standard heat of formation, AHºf, of phenol in kilojoules per mole at 25°C. (c) Calculate the value of the standard free-energy change, AG° for the combustion of phenol 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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