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 180^o 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 120^o to each other
• each sp² hybrid 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 109.5^o 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

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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:

Credits: www.inquirebotany.org

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

Credits: pharmacalc.blogspot.com

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   bond	Energy (KJ/mole)	Energy to break bonds (KJ/mole)
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   bonds	Energy (KJ/mole)	Energy to break bonds (KJ/mole)
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 pharmacalc823@gmail.com

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

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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.
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