Consider the following chemical reaction: C3H8(g) + H2(g) to give C2H6(g) + CH4(g) ΔH° = ? Calculate the enthalpy change for the reaction above using Hess's law Thermochemical data: H2(g) + 1\2O2(g) to give H2O(l) ΔH° =-285.8 kJ ΔH° combustion for CH4(g) ΔH° =-890.0 kJ/mol CO2 giving C(s, graphite) + O2(g) ΔH°= +393.5 kJ ΔH° combustion for C2H6(g) ΔH° =-1560.0 kJ/mol ΔH°f for C3H8(g) ΔH° =-103.8 kJ/mol
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.
Consider the following
C3H8(g) + H2(g) to give C2H6(g) + CH4(g) ΔH° = ?
Calculate the enthalpy change for the reaction above using Hess's law Thermochemical data:
H2(g) + 1\2O2(g) to give H2O(l) ΔH° =-285.8 kJ
ΔH° combustion for CH4(g) ΔH° =-890.0 kJ/mol
CO2 giving C(s, graphite) + O2(g) ΔH°= +393.5 kJ
ΔH° combustion for C2H6(g) ΔH° =-1560.0 kJ/mol
ΔH°f for C3H8(g) ΔH° =-103.8 kJ/mol
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