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The bond energy for H 2 O is the average energy required to break each of the two O–H bonds in sequence: Although the two bonds are the equivalent in the original symmetric molecule, the bond-dissociation energy of an oxygen–hydrogen bond varies slightly depending on whether or not there is another hydrogen atom bonded to the oxygen atom.
The energy required to break the bond is called the heterolytic bond dissociation energy, which is similar (but not equivalent) to homolytic bond dissociation energy commonly used to represent the energy value of a bond. One example of the differences in the energies is the energy required to break a H−H bond
The term bond-dissociation energy is similar to the related notion of bond-dissociation enthalpy (or bond enthalpy), which is sometimes used interchangeably.However, some authors make the distinction that the bond-dissociation energy (D 0) refers to the enthalpy change at 0 K, while the term bond-dissociation enthalpy is used for the enthalpy change at 298 K (unambiguously denoted DH° 298).
The triplet and singlet excitation energies of a sigma bond can be used to determine if a bond will follow the homolytic or heterolytic pathway. [2] A metal−metal sigma bond is an exception because the bond's excitation energy is extremely high, thus cannot be used for observation purposes. [2] In some cases, bond cleavage requires catalysts.
Bond cleavage is also possible by a process called heterolysis. The energy involved in this process is called bond dissociation energy (BDE). [2] BDE is defined as the "enthalpy (per mole) required to break a given bond of some specific molecular entity by homolysis," symbolized as D. [3]
Hydrolysis (/ h aɪ ˈ d r ɒ l ɪ s ɪ s /; from Ancient Greek hydro- 'water' and lysis 'to unbind') is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution , elimination , and solvation reactions in which water is the nucleophile .
Anhydridic bonds are often labelled as "high-energy bonds". P-O bonds are in fact fairly strong (~30 kJ/mol stronger than C-N bonds) [2] [3] and themselves not particularly easy to break. As noted below, energy is released by the hydrolysis of ATP. However, when the P-O bonds are broken, input of energy is required.
The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion or other chemical reaction. Thermal decomposition is a chemical reaction where heat is a ...