Bond enthalpy is the energy required to break a chemical bond between two atoms in a molecule. It can be used to determine heat transfer in chemical reactions and is expressed as kJ/mol. The breaking of the bond can occur via heterolysis or homolytic fission. Bond enthalpy also refers to the likelihood of a thermodynamic reaction and represents the amount of energy stored in a chemical bond. The enthalpy change within a system is measured by the amount of energy absorbed or released in endothermic or exothermic reactions.
Bond enthalpy is a term used in the study of thermodynamics that refers to the amount of energy required to break the chemical bond forged between any two atoms within a molecule. Since the strength of the bond varies between chemical reactions, the bond enthalpy values contained in the bond enthalpy table are given as averages. Usually, these values are expressed as kJ/mol, although they sometimes appear as kJ mol-1. Because this value can be used to determine the expected heat transfer in chemical reactions, it is sometimes used interchangeably with the terms bond dissociation enthalpy and bond dissociation energy.
The breaking of the chemical bond occurs in different ways. The fission or splitting of a neutral molecule resulting in an anion (negatively charged ion) and a cation (positively charged ion) has taken place via heterolysis. Conversely, if the bond breaking of a molecule causes two unpaired electrons, or free radicals, then the process has been initiated via homolytic fission.
In molecular chemistry, bond enthalpy also refers to the likelihood of a thermodynamic reaction within a system. One of the variables to consider for this potential is, of course, the strength of the bond. In general, the strongest bonds are found in the shortest formations since there are fewer molecules involved. Furthermore, for the reaction to be endothermic, the system must receive energy. Otherwise, with a loss of energy, the reaction would be defined as exothermic and would produce a new bond with a lower enthalpy.
Given the above, it can also be said that bond enthalpy represents the amount of energy stored in a chemical bond. Indeed, the heat exchange, or energy transfer, which occurs when a chemical reaction takes place can be calculated by reducing the value of the bond enthalpy by the amount of energy necessary to form the bond. In view of the chemical equation of a compound, enthalpy is an endothermic process that occurs on the reactant side of the formula. Conversely, the exothermic reaction, or the amount of energy required to create a chemical bond, is represented by the product side of the equation.
However, the total enthalpy of a system cannot be determined precisely unless it is a closed system. Since there are very few systems in total isolation, the enthalpy change within a system is calculated instead. How this change is directed depends on whether the chemical reaction is endothermic or exothermic. In the former, the enthalpy change is measured by the amount of energy absorbed into the system, as opposed to the amount of energy released in the latter. The value of the enthalpy change in both reactions is the same and is expressed as +ve or –ve.
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