A 110.1 gram sample of an unknown substance (MM = 189.50 g/mol) is cooled from 233.0 °C to 147.6 °C. (heat capacity of liquid = 1.62 J/g･°C; heat capacity of gas = 1.04 J/g･°C; ∆Hvap = 78.11 kJ/mol; normal boiling point, Tb = 160.3 °C) How much energy (in kJ) is absorbed/released to cool the gas?
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 110.1 gram sample of an unknown substance (MM = 189.50 g/mol) is cooled from 233.0 °C to 147.6 °C. (heat capacity of liquid = 1.62 J/g･°C; heat capacity of gas = 1.04 J/g･°C; ∆Hvap = 78.11 kJ/mol; normal boiling point, Tb = 160.3 °C) How much energy (in kJ) is absorbed/released to cool the gas?
Mass of the unknown substance= 110.1 g
Heat capacity of liquid = 1.62 J/g･°C
Heat capacity of the gas = 1.04 J/g.ºC
The given substance is cooled from Temperature: 233.0ºC -> 147.6ºC.
The complete process comprises of the following sub-processes:
Cooling the gas from 233.0ºC to 160.3ºC.
Condensation of the gas at its boiling point, Tb = 160.3ºC.
Cooling the liquid from 160.3ºC to 147.6ºC.
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