September 19, 2024, 02:26:54 PM
Forum Rules: Read This Before Posting

### Topic: calculating bond force constant.  (Read 18255 times)

0 Members and 1 Guest are viewing this topic.

#### khemauck

• New Member
• Posts: 8
• Mole Snacks: +0/-0
##### calculating bond force constant.
« on: March 21, 2015, 02:19:54 AM »
Hi,

I'm calculating the bond force constant of HCl as part of a lab for pchem. I've managed to calculate the reduced mass, and the value I have is 0.9801 amu or 1.62 x 10^27 kg.

However when it comes to the bond force constant I am completely stumped. It asks me 'calculate the bond force constant by substituting the midpoint freq into the expression containing the bond force constant' (k).

My midpoint value is 2890 wavenumbers (cm-1) which I converted into Hz by multipying by 3 x 10^10,
giving me 8.64 x 10^13 Hz.

I now have no idea what to do or which equation to use. This page (http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/vibrot.html) seems to have some clues but I just can't get my head around it.

If anyone could point me in the right direction it would be much appreciated!!

#### Corribus

• Chemist
• Sr. Member
• Posts: 3526
• Mole Snacks: +540/-23
• Gender:
• A lover of spectroscopy and chocolate.
##### Re: calculating bond force constant.
« Reply #1 on: March 21, 2015, 10:01:54 AM »
Hate to just throw up a link, but the appropriate equation to use can be found here:

http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Infrared_Spectroscopy/Infrared%3A_Theory

Although, it can be found in the link you provided as well.

If you have the equilibrium frequency and the reduced mass, you can easily calculate the force constant using the equation that contains only these three variables.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman