A 0.500-g sample of n-heptane(ℓ) burned in a constant volume calorimeter to CO2(g) and H2O(ℓ) causes a temperature rise of 2.934 °C. If the heat capacity of the calorimeter and its accessories is 1954 cal/°C, and the mean temperature of the calorimeter is 25 °C, calculate: (a) The heat of combustion per mole of the heptane at constant volume; (b) The heat of combustion of the heptane per mole at constant pressure.
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 0.500-g sample of n-heptane(ℓ) burned in a constant volume calorimeter
to CO2(g) and H2O(ℓ) causes a temperature rise of 2.934 °C. If the heat
capacity of the calorimeter and its accessories is 1954 cal/°C, and the mean
temperature of the calorimeter is 25 °C, calculate:
(a) The heat of combustion per mole of the heptane at constant volume;
(b) The heat of combustion of the heptane per mole at constant pressure.
Thermochemistry( answers must be a) ∆U = –1149 kcal; ∆H = –1151 kcal )
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