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.
Define the terms bond enthalpy and mean bond enthalpy.
Use examples to illustrate the difference between the two quantities.
The bond enthalpy of a chemical bond can be defined as the total amount of energy required to break 1 mole of that chemical bond. For example, the bond enthalpy of the oxygen-hydrogen single bond is equal to 463 kJ/mol. This implies that a total of 463 kilojoules of energy is required to break 1 mole of hydrogen-oxygen single bonds.
To express the strength of a single, specific bond in a molecule, the quantity ‘mean bond enthalpy’ or ‘average bond enthalpy’ can be used. The mean bond energy of a chemical bond (in a molecule) can be determined by calculating the average value of all the bond dissociation energies of that type of bond in the molecule.
If a molecule has several bonds, bond enthalpy is calculated for each bond and the average value has been considered. For example, methane (CH4) has four C-H bonds, and the average bond energy is +1652 kJ and +415.5kJ per mole of the bond.
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