Content Curator
Bond energy as an estimation of the bond strength needed to part one mole of a particle into its constituent atoms. It is also known as the bond enthalpy or average bond enthalpy. Bond energy can be said to be directly proportional to the stability of that particular chemical bond.
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Bond Energy
A chemical compound is made up of different types of atoms. A chemical link holds these atoms together. Chemical bonds are created between atoms when electrons are transferred or valence electrons are shared. The bond energy is useful in thermochemistry because it may be used to calculate the enthalpy of various chemical reactions, such as burning. The enthalpy of reaction is the difference between bond breaking and bond forming during a chemical process.
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Comparative Difference between Bond Dissociation Energy and Bond Energy
A chemical bond's bond dissociation energy (abbreviated BDE) is defined as the change in enthalpy associated with the chemical bond's rupture by homolytic cleavage. The amount of energy necessary to aid the homolytic breakage of the bond between A and B, leading in the creation of two free radicals, is the bond dissociation energy of a molecule A-B, for example. It's vital to remember that the bond dissociation energy of a chemical bond is determined by the environment's absolute temperature.As a result, the bond dissociation energy is often estimated under ordinary circumstances (where the temperature is roughly equal to 298 Kelvin). On the other hand, the bond energy of a chemical bond in a compound is equal to the sum of all the bond dissociation enthalpies of that link in the molecule.
Read Also: Standard Enthalpy of Formation
Different Bond Energies
A covalent bond is set up when connected iotas in an atom share electrons similarly. With an increment in the quantity of connections between connected molecules, the energy or strength of a synthetic bond increases. As such, when the bond request expands, the synthetic bond's solidarity builds, raising the bond energy much higher. Bond energies of a solitary, twofold, and triple covalent connection between carbon iotas, for instance, are as per the following:
Bond Energies
| Covalent Bond | Bond Energy |
|---|---|
| C-C | 348 kJ//mol |
| C=C | 614 kJ//mol |
| C≡C | 839 kJ//mol |
Chemical bonds with various atoms have varying bond energies:
Bond energy is also affected by the atomic scale of the bound atoms. The bond length grows as the atomic size of bound atoms increases, lowering the bond energy of the given covalent connection. Moving down in the group from F to I, for example, increases atomic size, therefore bond length increases from HF to HI and bond energy falls in the same sequence.
| Covalent Bond | Bond Energy |
|---|---|
| H-F | 568 kJ//mol |
| H-CI | 432 kJ//mol |
| H-Br | 366 kJ//mol |
| H-I | 298 kJ//mol |
Effect of Polarity on Bond Energy.
The extremity of a fortified particle affects the bond energy of a synthetic bond. As the extremity distinction between associated particles enlarges, the fascination power between them fabricates, expanding the bond energy. The bond energy of the H-F bond is higher than the bond energy of the H-Cl bond since F is more electronegative than Cl. The H-F bond is in this way more grounded than the H-Cl bond.
Likewise, when the quantity of solitary sets on associated atoms increases, so does the shock between them, bringing down the bond energy of the substance bond. The bond energy of N with H is bigger than that of O since O has two solitary sets though N just has one.
Examples
| Covalent Bond | Bond Energy |
|---|---|
| H-N | 391 kJ//mol |
| H-O | 466 kJ//mol |
| H-F | 568 kJ//mol |
| H-CI | 432 kJ//mol |
| H-BR | 366 kJ//mol |
| H-I | 298 kJ//mol |
Factors Affecting Bond Energy
Bond energy is a measurement of a bond's strength. The bond's strength is determined by the following elements.
- Electronegativity difference of bonded atom
- Atomic Dimension
- Bond length
Difference in Electronegativity of Bonded Atoms
The bond energies of H-X sort compounds, where X= F, Cl, Br, I, are not uniformly split between the bound molecules, for example HX. The reinforced pair is more drawn to the X molecule as the halogen iota turns out to be more electronegative, and thus extremity creates. This results in an expansion in the appealing power for restricting.
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Atomic Dimensions
The size of an atom and the dissolution of bonds have a direct relationship. The smaller the atom's atomic size, the less energy is required to break the bond. For instance, because iodine is larger than the other halogens, it has a low attraction from the nucleus and outermost orbit. To break the bond, only a minimal amount of energy is necessary.
The Length of the Bond
The bond length is the distance between the nuclei of two atoms that form a covalent bond. Physical approaches are used to determine the bond lengths. Electron diffraction, X-ray diffraction, and spectrum investigations are some of the techniques used. The length of a covalent link between two atoms is often, but not always, independent of the molecule's composition.
Read More: Valency of Carbon (Tetravalency)
Things to Remember based on Bond Energy
- Bond energy is a part of CBSE Class 11 first term syllabus, unit 4, Chemical Bonding and Molecular Structure.
- It carries a total of 14 periods and 6 marks.
- Bond energy helps in the measurement of strength of a chemical bond.
- It also helps in understanding the stability obtained when there is bond formation between two atoms.
- Bond energy can be denoted by ΔH
- Bond energy calculation can be denoted by: ∑H(bond broken)- H(bond formed)
Sample Question based on Bond Energy
Ques 1. Question-Using the following reaction equation and the provided data, calculate the bond energy of a BrF bond.
(ΔHf of BrF5(g)=−429kJ/mol, ΔHf of Br(g)=112kJ/mol, ΔHf of F(g)=79kJ/mol)
Br(g)+5F(g)→BrF5(g)
- 936kJ/mol
- 187kJ/mol
- 86kJ/mol
- 47kJ/mol
Ans. Formula Applied:
ΔHtotal=ΔHproducts−ΔHreactants
Substituting the given values, we get:
ΔHtotal=(−429)−(−112+(5×79))
ΔHtotal=(−429)−(−112+(5×79))
On solving, we get:
ΔHtotal=−936kJ/mol
ΔHtotal=−936kJ/mol
This is equal to the bond energy of the entire BrF5 molecule. Because there are five BrF bonds in it, a single BrF bond's bond energy is one-fifth of the total bond energy.
⇒B.E=936/5
=187kJ/mol
Hence the correct option is option b).
Ques 2. How do you calculate the bond energies? (3 marks)
Ans. Following are the steps to calculate bond energies:
- Firstly, all the bond energies of the bonds present in the reactants need to be added and is called the energy in.
- Secondly all the bond energies of the bonds present in the products need to be added and is called the energy out.
- Finally calculate the change in the energy by subtracting energy out from energy in.
Ques 3. What are the factors that affect bond energy? (3 marks)
Ans. Factors affecting the bond energy are:
- Electronegativity difference of bonded atom
- Atomic Dimension
- Bond length
Ques 4. What is bond energy? (2 marks)
Ans. Bond energy can be referred to as an estimation of the bond strength needed to part one mole of a particle into its constituent atoms. It is also known as the bond enthalpy or average bond enthalpy. Bond energy can be said to be directly proportional to the stability of that particular chemical bond.
Ques 5. What is the use of bond energy? (2 marks)
Ans. The bond energy is useful in thermochemistry because it may be used to calculate the enthalpy of various chemical reactions, such as burning. The enthalpy of reaction is the difference between bond breaking and bond forming during a chemical process.
Ques 6. Explain the major difference between bond dissociation energy and bond energy. (2 marks)
Ans. The major difference between bond dissociation energy and bond energy is:
Bond dissociation energy: It refers to the quantity of energy needed to dissociate a particular bond through homolytic cleavage.
Bond energy: It refers to the average quantity of energy needed in order to disintegrate all the bonds of a compound between two atoms which are alike in nature.
Ques 7. The bond energy ( in kcal mol−1) of a C-C single bond is approximately: (1 mark)
(A) 1
(B) 10
(C) 100
(D) 1000
Ans. C, 100.
Ques 8. What does bond energy depend on? (1 mark)
Ans. Bond energies depend on the number of bonds between atoms.
Ques 9. Why is the enthalpy change always positive when the chemical bond is broken? (2 marks)
Ans. The process associated with the breaking of a bond is always endothermic in nature because the energy should be transferred to the molecules so as to break the bond present in it. Hence the enthalpy change is always positive when the chemical bond is broken.
Ques 10. What is bond strength? (1 marks)
Ans. Bond strength can be referred to as the strength with which every atom is attached with one another. It states how much energy is needed in order to break the atomic bond between two atoms.
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