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  • Sunday 23 July 2017

    Bond Energy Calculations

    Hello guys......!!!

    After a long gap i'm back with some calculations stuff here today, which i was supposed to present you guys a long ago, but as per my experience which i had with current process engineers made me put those under hold, and i think today i gotta a solid reason for posting this, as i've seen some guys who were striving hard to learn this stuff, which is not that much clear on the web.

    But before that you have to grab some technical vocabulary,

    What is Bond Energy ?

    Energy to break a bond(simply dissociation) and convert the mole of molecules into simple atoms is known as bond Energy, sometimes referred as Bond Enthalpy.

    And different bonds will have different energies, as like most of you know.

    Bond Enthalpy Values ?
    The bond enthalpy values is the value of the energy (the unit is in kJ/mol) required to break a particular chemical bond at a temperature of 298 K or 25 degrees Celsius. For each chemical bond, there are different values of bond enthalpies.
    What is a Double bond ?

    A chemical Bond in which two pair of electrons were shared between two atoms, upto this everyone can remember, but the thing that some of us forget is a Double bond consists of one Sigma Bond and one Pi Bond.

    After reading this you may Google for Sigma Bond and Pi Bond, for you it is below,

    What is Sigma Bond ?

    A Sigma bond is formed due to head on overlapping of orbitals

    By default, Sigma bonds were stronger than Pi bonds.

    What is Pi Bond ?

    If i'm right, by now you have recollected the definition of a Pi bond, any way, a Pi -bond is formed due to lateral overlapping of P orbitals.

    I think right now you are clear about Sigma bond and a Pi bond, So now lets move to next level,

    What is Triple Bond ?

    A Triple bond is a chemical bond between two atoms involving six bonding electrons instead of usual two in a covalent single bond. A triple bond consists of 1 Sigma bond and 2 Pi bonds.

    What is Valency ?

    The combining capacity of atom is simply referred as Valency,

    This is the important thing which can be defined in single line but needs some focus to understand, so better to get some exercise to make it clear.

    Combine Capacity: An element’s combining capacity is the number of electrons it needs to gain or lose in order to be a stable ion.

    Metals lose electrons. (positive ion CATION) 
    Non-metals gain electrons. (negative ion ANION)

    If you ever want to calculate valency, then better go with Lewis diagrams.

    Lewis Diagrams were shown below:

    For preparing these Lewis Diagrams, you should be able to recollect the Inert atoms in periodic table, becoz if you see above fig. He atom is having 2 dots, and Li is having 1 dot, the same case is with Ne atom and Na atom, that means dots will appear to reduce after crossing an inert atom. 

    Lets get back to Combining capacity of some electrons, which are presented in the attached files, click this COMBINING CAPACITY OF ELEMENTS.PDF

    Now, upto my knowledge, you have reached 70%. one more topic left, i.e., Hybridisation.

    What is Hybridisation ?

    Hybridization happens when atomic orbitals mix to form new atomic orbitals. The new orbitals have the same total electron capacity as the old ones. The properties and energies of the new, hybridized orbitals are an 'average' of the original unhybridized orbitals.

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    What is SP Hybridisation ?

    When a C atom is attached to 2 groups and so is involved in 2 sigma bonds, it requires 2 orbitals in the hybrid set. This requires that it is sp hybridised.

    Simple Characteristics:

    • sp occurs when a C has 2 attached groups
    • sp has 50% s and 50% p character
    • the 2 sp hybrids point in opposite directions at 180o to each other
    • each sp hybrid is involved in a s bond
    • the remaining p orbitals forms the 2p bonds
    • view a triple bond as a s + 2p bonds

    What is SP2 Hybridisation ?

    When a C atom is attached to 3 groups and so is involved in 3 s bonds, it requires 3 orbitals in the hybrid set. This requires that it is sp2 hybridised.

    Simple Characteristics:

    • sp2 occurs when a C has 3 attached groups
    • sp2 has 33% s and 67% p character
    • the 3 sp2 hybrids point towards the corners of a triangle at 120o to each other
    • each sphybrid is involved in a s bond
    • the remaining p orbital forms the p bond
    • view a double bond as a s + p bond

    What is SP3 Hybridisation ?

    Overlapping of one S orbital and 3 P orbitals will result in SP3 hybridisation.

    Simple Characteristics:

    • sp3occurs when a C has 4 attached groups
    • sp3 has 25% s and 75% p character
    • the 4 sp3 hybrids point towards the corners of a tetrahedron at 109.5o to each other
    • each sp3hybrid is involved in a σ bond.

    This is enough for getting into the Bond energy Calculation, Lets begin the show,

    Bond energies of some elements were presented below:

    For More Bond Energies Click this BOND ENERGIES.PDF
    Example - 1:  H2  +  Cl2    --------->    2 HCl

    Now the first step is to make the reaction and bonds looks simpler.

    H - H  +  Cl - Cl   ----------->   H - Cl  +  H - Cl

    From above mentioned table, the average bond energies were 

    H - H = 432 KJ/mole, Cl - Cl = 243 KJ/mole, H - Cl = 427 KJ/mole,

    H(R) = 432 + 243 = 675 KJ/mole,
    H(P) = 2 x 427 = 854 KJ/mole,

    ΔH = H(R) - H(P) = 675 - 854 = - 179 KJ/mole

    - indicates exothermic reaction.

    As like mentioned previously, here now i'm presenting an example of a synthesis reaction,

    Actually the reason behind sharing this example is that i got an mail from one of the process engineer working in a reputed MNC, mentioning that i'm not presenting any value added examples, so on his request to perform Bond energy calculation for Aspirin Manufacturing, I'm presenting the below example:

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    EXAMPLE - 1 :

    Synthesis Scheme of Aspirin Manufacturing:

    Now we need to visualize the bonds by breaking them, like shown below:


    Now count the number of bonds in reactants side and products side as shown below: 

    Bond Reactants Products
    C - H 10 13
    C = C 3 3
    C = O 3 1
    O - H 2 1
    C - C 6 4
    C - O 3 5

    Now calculate the energy released while breaking bonds, i mean bond dissociation energy,

    Bond Reactant
    Energy to
    break bonds
    C - H 10 413 4130
    C = C 3 614 1842
    C = O 3 745 2235
    O - H 2 467 934
    C - C 6 347 2082
    C - O 3 358 1074

    So, total energy required for breaking reactants side bonds is 

    H(R) = 4130 + 1842 + 2235 + 934 + 2082 + 1074 = 12297 KJ/mole,

    Now calculate the energy required to make products side bonds,

    Bond Product
    Energy to
    break bonds
    C - H 13 413 5369
    C = C 3 614 1842
    C = O 1 745 745
    O - H 1 467 467
    C - C 4 347 1388
    C - O 5 358 1790

    So, total energy required for making Products side bonds is 

    H(P) = 5369 + 1842 + 745 + 467 + 1388 + 1790 = 11601 KJ/mole,

    Now, its time to know what amount of energy will be released / consumed,

    dH = H(R) - H(P) = 12297 - 11601 = + 696 KJ / mole.

    + indicates reaction is Endothermic, 

    And for mole of manufacturing we need to supply 696 KJ.

    Note: More examples will be updated based on request. you can use contact me tab or Contact us button available on top left, or mail me at

    That's it......!!!

    If you understand Say Cheers.......!!! Still queries feel comfortable to message me, or comment here....!!

    Calculation sheet Will be updated within a week, stay tuned for more.......!!!!

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    About The Author

    Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
    Follow Me on Twitter AjaySpectator & Computer Innovations


    1. hie...
      i am following and using ur Calculation it is very useful.
      Can you share Cooling tower blow down calculation??

      1. Dear Ramachandra,

        Usually, the main motto of blowdown is to remove the TDS, and it can be determined if you know two out of three parameters, those three were: Cycles, Evaporation, makeup water.

        Blowdown = Evaporation / ( Cycles - 1 ),
        = Makeup - Evaporation,
        = Makeup / Cycles.

        Cycles = (Total Dissolved solids in makeup water) / (Total Dissolved solids in blowdown),

        Any queries feel free to comment/message.

        AJAY K

    2. Dear Ajay,
      Can you calculate theoretically time required for completion of particular reaction???

      1. Dear Mahesh,

        There wont be any calculation to find out the time required, all we can do is having trials and checking the extent of reaction.

        But as per thermodynamics we can calculate the extent of reaction based on order or reaction and the critical temperature and pressure.

        AJAY K

    3. Hi, Ajay
      i am following your calculation its very usefull for me,

      Can you please share me Dryer selection & sizing calculation

      1. Hii Sakthikumaran,

        Added the topic in the list of future posts, i'll share it.

        Best Regards,
        AJAY K

    4. how we can found order of reaction in Pharma?? can we use order op reaction for any optimization calculation??

    5. Dear Ajay,
      Why you cakcalcule bond energy only for know about exothermicity and endothermicity ,if you know bond energy is 696kj/mol then what should we do in practical approach .
      How bond energy help us in manufacrturing process ?.and which calculation .


      1. Dear Raj,

        Pl refer the below post, it will helpful to clear your query, In the below post instead of the exothermicity obtained from RC1e use the energy derived from bond energy.
        Refer link:

        AJAY K

    6. thanks for such an informative post.
      sir If I have a reaction mass at temperature of 120C and I am adding sulphuric acid to the reaction mass at that temperature then will this method hold for that situation, because the values are at room temperature and my addition is at quite a higher temperature. I wanted to know the exothermicity of the reaction at the time of addition.

      1. Hii Rajesh,

        Pl tell me the reaction involved between the H2SO4 and the active intermediate in the reaction mass.
        The bond dissociation energy won't remain the same and will vary based on temperature. But if the similar bonds were breaking or forming on both reactants and products side, then the overall heat of reaction based on group contribution method will remain same.
        If some different bonds were forming on the products side then there will be slight variation in the heat of reaction, so in that case you can consider 30% excess to that of RT.

        Any queries feel free to comment or reach me at

        Best Regards,
        AJAY K


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    Hi! I am Ajay Kumar Kalva, owner of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.

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