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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 Morse potential, named after physicist Philip M. Morse, is a convenient interatomic interaction model for the potential energy of a diatomic molecule.It is a better approximation for the vibrational structure of the molecule than the quantum harmonic oscillator because it explicitly includes the effects of bond breaking, such as the existence of unbound states.
This sum will have a maximum at , representing the point of bond dissociation; summing over all the differences up to this point gives the total energy required to dissociate the molecule, i.e. to promote it from the ground state to an unbound state. This can be written:
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.
Homolytic cleavage is driven by the ability of a molecule to absorb energy from light or heat, and the bond dissociation energy . If the radical species is better able to stabilize the radical, the energy of the SOMO will be lowered, as will the bond dissociation energy. Bond dissociation energy is determined by multiple factors: [4]
This periodic order also follows the atomic radius of halogens and the length of the carbon-halogen bond. For example, in the molecules represented by CH 3 X, where X is a halide, the carbon-X bonds have strengths, or bond dissociation energies, of 115, 83.7, 72.1, and 57.6 kcal/mol for X = fluoride, chloride, bromide, and iodide, respectively. [2]
The H–I bond dissociation energy is likewise the smallest of the hydrogen halides, at 295 kJ/mol. [5] Aqueous hydrogen iodide is known as hydroiodic acid , which is a strong acid. Hydrogen iodide is exceptionally soluble in water: one litre of water will dissolve 425 litres of hydrogen iodide, and the saturated solution has only four water ...
It is a chocolate-brown solid that decomposes at 0 °C, [1] disproportionating to elemental iodine and iodine pentafluoride: 5 IF → 2 I 2 + IF 5. However, its molecular properties can still be precisely determined by spectroscopy: the iodine-fluorine distance is 190.9 pm and the I−F bond dissociation energy is around 277 kJ mol −1.