The heat of reaction for a chemical reaction can be calculated by finding the sum of the bond energies of the products and subtracting that from the sum of the bond energies of the reactants: Heat of reaction==Sum of the energy for the bonds broken − Sum of the energy for the bonds formedSum of reactant bond energies − Sum of product bond energiesHeat of reaction=Sum of the energy for the bonds broken − Sum of the energy for the bonds formed=Sum of reactant bond energies − Sum of product bond energies When calculating the sum of the bond energies, each bond in the reaction must be accounted for. For example, CH4CH4 is a reagent with a coefficient of 1 in the reaction. There are four C−HC−H bonds in methane and one methane molecule per reaction, for a total of four C−HC−H bonds on the reactant side. All four bonds must be accounted for when finding the sum of the bond energies for the reactants. Calculate the heat of reaction using the average bond dissociation energies given in the introduction and your answer to Part B for the reaction CH4 + 2O2 → CO2 + 2H2O
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.
The heat of reaction for a
Heat of reaction==Sum of the energy for the bonds broken − Sum of the energy for the bonds formedSum of reactant bond energies − Sum of product bond energiesHeat of reaction=Sum of the energy for the bonds broken − Sum of the energy for the bonds formed=Sum of reactant bond energies − Sum of product bond energies
When calculating the sum of the bond energies, each bond in the reaction must be accounted for. For example, CH4CH4 is a reagent with a coefficient of 1 in the reaction. There are four C−HC−H bonds in methane and one methane molecule per reaction, for a total of four C−HC−H bonds on the reactant side. All four bonds must be accounted for when finding the sum of the bond energies for the reactants.
Calculate the heat of reaction using the average
CH4 + 2O2 → CO2 + 2H2O
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