Bond energy and bond dissociation enthalpy may sound like they mean the same thing but they don’t.
Even though they are both thermodynamic properties of a specific system that comes under scrutiny, their energy uses are different.
Sometimes both terms are commonly grouped under the umbrella term standard enthalpy change to define them both. They both give an energy value after bond cleavage.
Key Takeaways
- Bond energy is the average energy required to break a specific type of bond in a molecule. In contrast, bond dissociation energy is needed to break a single bond in a particular molecule.
- Bond energy is an average value, whereas bond dissociation energy is a specific value for individual molecules.
- Bond energy values help predict the stability of molecules, while bond dissociation energy is useful in understanding reaction mechanisms and thermochemistry.
Bond Energy vs Bond Dissociation Energy Enthalpy
Bond energy is a measure of bond strength and is the amount of energy released or absorbed when a bond is formed, referring to the energy required to form a chemical bond. Bond dissociation energy enthalpy measures bond stability and the amount of energy required to break a bond.
Bond energy is the average value of all the bonds that are broken in a system.
For example, if in a specific thermodynamic environment, ten bonds are awaiting to be broken, then the bond energy value that is calculated after all the bonds have been broken would be the sum of individual energy released divided by ten.
Bond dissociation energy is a single value that need not be further calculated after the cleavage and release of the required energy.
In a thermodynamic environment, after a bond between two atoms in a molecule or compound is broken, a small amount of energy is released, and this single energy unit is called bond dissociation energy enthalpy.
Comparison Table
| Parameters of Comparison | Bond Energy | Bond Dissociation Energy Enthalpy |
|---|---|---|
| Represented By | E | H |
| Specificity | Any number of bonds can be broken with no limit | Only a single cleavage value |
| Value | Average value | Single and specific |
| Measures | Bond strength | Individual cleavage properties |
| Used for | Formation of atoms | Formation of free radicals |
What is Bond Energy?
The breaking of the bond between two atoms that are in the gaseous phase of the state releases a certain amount of energy.
This when repeated for an entire compound has many values of energy that are released.
An average of all the energy released is called the bond energy of a specific thermodynamic system.
It could also be defined as the energy to break down all the bonds that are present in a system to create a free atomic system.
The optimum temperature for carrying out such a cleavage to release the bond energy is 298K.
But this temperature can vary depending upon the pressure around a system or even the compound’s molecular nature.
A graph that could indicate the bond energy is between the potential energy of a system and the distance between the atoms in question.
A possible outcome of such a graph is the distances at which the energy required is either too much or too little.
This distance shown also gives the bond length between two atoms in a theoretical form.
The greater the bond energy, the higher is the bond strength and the lesser is the distance between them.
In chemistry, bond energy is represented with the English alphabet E for ease.
The bond energy is used to form all the atoms that might come in useful in a later reaction that might even be a part of a cascade reaction.
There is a single carbon molecule and four hydrogen molecules. The reaction involved is breaking CH4 into its individual five atoms.
The eventual and average energy value released is the bond energy, which is 414KJ/mol.
What is Bond Dissociation Energy Enthalpy?
Bond Dissociation Energy is commonly referred to as standard enthalpy.
The energy released is due to the breaking of the covalent bond.
Covalent bonds are those bonds present between nonmetallic atoms that are formed due to the sharing of electrons between atoms.
Bond dissociation energy is released only after the atoms are cleaved by homolysis.
Homolysis refers to the breakdown of molecules into equal structured particles, which are free radicals.
Another definition of bond dissociation energy is the changes in the enthalpy that occurs due to the cleavage of a molecule by the process of hemolysis.
The bond dissociation energy is associated with individual cleavages.
No sum of all cleavages happening in a thermodynamic system gives the bond dissociation energy.
It is represented by the English letter H to make the word easier to use.
The major function of bond dissociation energy is to create the energy needed for the formation of free radicals that come into use in other reactions.
For example, there are four different bond enthalpies in the complete dissociation of a methane(CH4) molecule.
The four enthalpies are needed to break the four existing bonds in the system to create four free radicals.
This shows that the energy values are different for breaking bonds in a single molecule.
Main Differences Between Bond Energy and Bond Dissociation Energy Enthalpy
- While bond dissociation energy always gives the energy value of a single bond cleavage, whereas, in the case of bond energy, the energy given or released is the average of all the cleavage values of a system.
- The alphabet E represents Bond energy, while the letter H represents bond dissociation energy enthalpy.
- During the cleaving of methane, four bond dissociation energy values are 439, 469,423, and 339 KJ/mol, but it has a singular bond energy value of 414 KJ/mol.
- The energy value would vary in bond energy, but it wouldn’t in the case of bond dissociation enthalpy, as it is calculated for individual cleavages.
- There is a specificity in the case of bond dissociation enthalpy as it can have only one bond, while there is no specificity for bond energy as it is an average.
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