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EK Lesson 2.7 Questions 25-32
Olivia_5618
#1 Posted : Friday, June 19, 2020 8:00:17 PM
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I'm having a bit of trouble understanding the definitions of high/low energy and what that means for stability and therefore strength of a molecule/bonds from the EK textbook;

What I have gathered from the EK text:

Having a HIGH BOND ENERGY (aka avg. Bond strength) means you have a MORE STABLE BOND because it requires more energy to break the bonds according to the answer key for Q. 25.

However, A SIGMA BOND is the STRONGEST type of bond but is the bond with the LOWEST ENERGY? PI BONDS are HIGH ENERGY (which makes sense because they are overlapping p-orbitals vs. sp as seen in sigma) but are WEAKER THAN SIGMA BONDS? Doesn't this completely contradict what was said in the above statement as outlined by EK text?

I just am looking to have these kinds of definitions down pat to make it easier to understand MCAT tricky questions.

Thank you :)

INSTR_Katerina_102
#2 Posted : Sunday, June 21, 2020 4:25:43 PM
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Hey,

These are all great points.

"Having a HIGH BOND ENERGY (aka avg. Bond strength) means you have a MORE STABLE BOND because it requires more energy to break the bonds according to the answer key for Q. 25." -yep, good summary


However, A SIGMA BOND is the STRONGEST type of bond but is the bond with the LOWEST ENERGY? PI BONDS are HIGH ENERGY (which makes sense because they are overlapping p-orbitals vs. sp as seen in sigma) but are WEAKER THAN SIGMA BONDS? Doesn't this completely contradict what was said in the above statement as outlined by EK text?

Energy is dependant on perspective - from the first point we are talking about energy needed to break bonds which is bond energy. The second perspective is that of potential energy - the energy level of the bond itself. To need a lot of energy to break a bond (bond energy) implies that it is in a LOW ENERGY state (potential energy). And to need not a lot of energy to break a bond (bond energy) implies it is in a HIGH ENERGY state (potential energy).

Keep in mind bond energy = -potential energy from bonding - that is you give up the potential energy you could have used for other things to bond.


Let me know if you need any further clarification.
INSTR_Katerina_102
#3 Posted : Sunday, June 21, 2020 4:38:55 PM
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Molly also provides a great analogy for this in the Chemistry forum, I'll try to link it here:

https://portal.prep101.c...Chem-EK-Q25-Page-47.aspx
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