Bond Dissociation Enthalpy

It is possible to define bond dissociation enthalpy as the standard change in enthalpy that occurs when a bond is cleaved via homolytic fission. The radicals that are formed as a result of the homolysis of the bond are the most common.

Bond Dissociation Enthalpy

The bond dissociation enthalpy of a chemical bond between two species can be used to estimate the strength of the chemical bond between the two species. It is often defined as the enthalpy change of the homolytic fission of a chemical bond at absolute zero, although it is typically measured as the enthalpy change at standard conditions (298K) (0K).

Features  of bond dissociation enthalpy

It is the amount of energy that must be supplied in order to break a chemical bond that exists between two different species of organism.

Chemical bond strength can be calculated through the use of this method.

With regard to diatomic molecules in particular, it is equal to the value of bond energy.

The bond between silicon and fluorine is said to have the highest bond dissociation enthalpy of all the chemical bonds known.

Covalent bonds between atoms or molecules are said to have low bond dissociation energies because they are formed by electrostatic attraction.

For diatomic molecules, as previously discussed, the bond dissociation enthalpy is equal to the bond energy, which means that the bond energy is conserved. This is due to the fact that bond energy is the average value of all the bond dissociation enthalpies of all bonds of the same type in a molecule, and bond energy is calculated as follows:

To illustrate, consider a molecule of methane from which all hydrogen atoms must be removed in order to complete the transformation. The energy required to remove the first hydrogen molecule is 105 kcal/mol, whereas the energy required to remove the second hydrogen molecule is 110 kcal/mol. It is calculated that the bond dissociation enthalpy of the third and fourth hydrogens is 101 kcal/mol and 81 kcal/mol, respectively, for these hydrogens. By averaging these values, it is discovered that the total bond energy is 99 kcal/mol, which is not equal to any of the bond dissociation energies of the C-H bonds, as previously stated.

Difference between bond enthalpy and bond dissociation enthalpy 

It should be noted that there is a significant difference between bond enthalpy and bond dissociation enthalpy, which is demonstrated below.

With the exception of diatomic molecules, the bond-dissociation enthalpy is diametrically opposed to the bond enthalpy. For a given molecule, the bond-dissociation enthalpy represents the energy required to dissociate one single chemical bond, whereas the bond enthalpy represents an average of all the bond-dissociation enthalpy of the bonds of a similar type for that molecule. For a homoleptic compound EXn, the enthalpy change of the response EXn →  E + nX increases the enthalpy change of the E–X bond by a factor of (1/n). As a result, Bond Enthalpy can also be referred to as Average Bond Dissociation Enthalpy, and Bond Dissociation Enthalpy can be referred to as Standard Enthalpy of Dissociation, and Bond Enthalpy can also be referred to as Standard Enthalpy of Dissociation.

Unless otherwise stated, the average bond enthalpies given in tables are normal estimations of the bond enthalpy of an assortment of species categories containing “typical” instances of the bond under consideration. To break a HOH bond in the water molecule (H2O), for example, it takes 118.8 kcal/mol (497.1 kJ/mol) of energy. The separation of the remaining hydroxyl requires 101.8 kcal/mol (425.9 kJ/mol) of energy. According to conventional wisdom, the enthalpy of the O-H covalent bonds in water is 110.3 kcal/mol (461.5 kJ/mol), which is essentially the average of these values.

For the elimination of progressive hydrogen atoms from methane, the bond-dissociation enthalpies are as follows: D(CH3-H): 110 kcal/mol (460 kJ/mol), D(CH2-H): 101 kcal/mol (423 kJ/mol), and D(CH-H): 81 kcal/mol (339 kJ/mol) The bond enthalpy is calculated as 99 kcal/mol or 414 kJ/mol in this manner (the normal of the bond-dissociation enthalpies). None of the individual bond-dissociation enthalpies approaches the bond energy of 99 kcal/mol, which is the maximum possible.

The Chemical Bonds with the Weakest and the Strongest Strengths

The concept of bond dissociation enthalpy can be used to identify the chemical bonds that are the weakest and the strongest. As previously discussed, the bond between silicon and fluorine is found to be the strongest chemical bond ever discovered.

In a silicon tetrafluoride molecule, it is estimated that the bond dissociation energy required to break the first silicon-fluorine bond is 166 kcal/mol, or 166 kcal/mol. Due to the large difference in electronegativities between silicon and fluorine atoms, as well as the fact that fluorine is the most electronegative element in the entire periodic table, this can be explained.

Moving on to neutral compounds, it is discovered that the carbon-oxygen bond in carbon monoxide has the highest strength of any known bond, with a bond dissociation energy of 257 kcal/mol. It should be noted that the carbon-carbon bond in ethyne possesses a relatively high bond dissociation energy, which is estimated to be approximately 160 kcal/mol.

Consequently, the concept of bond dissociation enthalpy has been found to be extremely useful in the field of thermochemistry, as previously stated.

CONCLUSION

It is possible to define bond dissociation enthalpy as the standard change in enthalpy that occurs when a bond is cleaved via homolytic fission. The radicals that are formed as a result of the homolysis of the bond are the most common.The bond dissociation enthalpy of a chemical bond between two species can be used to estimate the strength of the chemical bond between the two species. It is often defined as the enthalpy change of the homolytic fission of a chemical bond at absolute zero.It is the amount of energy that must be supplied in order to break a chemical bond that exists between two different species of organism.Consequently, the concept of bond dissociation enthalpy has been found to be extremely useful in the field of thermochemistry.