The heat of fusion of heptane (C7H16) at its normal melting point of -91°C is 14.0 kJ/mol, while its heat of vaporization at its normal boiling point of 98°C is 31.9 kJ/mol. (a) Use these data to calculate the heat of sublimation for C7H16. ____kJ/mol Is your answer precise or is it approximate? (b) At 298 K, the standard heat of formation of C7H16(l) is -224.2 kJ/mol while the standard heat of formation of C7H16(g) is -187.6 kJ/mol. Use this to calculate the heat of vaporization of heptane. kJ/mol. Is the result for part (b) larger or smaller than the value given in the statement of the problem?
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) Use these data to calculate the heat of sublimation for C7H16. ____kJ/mol
Is your answer precise or is it approximate?
(b) At 298 K, the standard heat of formation of C7H16(l) is -224.2 kJ/mol while the standard heat of formation of C7H16(g) is -187.6 kJ/mol. Use this to calculate the heat of vaporization of heptane. kJ/mol.
Is the result for part (b) larger or smaller than the value given in the statement of the problem?
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