Re: [Phys-L] Energy & Bonds

[Dr Keith S Taber <kst24@cam.ac.uk>]

Hi Paul

Well, the way I understand it (and I'd be interested to see if I'm in a 
minority) the convention is that the nominal zero is infinite separation 
(zero force acting), and the formula you give relates to how far below 
the nominal zero - so the formula as you have it is the energy needed to 
separate to infinity (which of course does get larger as r gets smaller).

Remember that in your formula you have q and q - these need to have 
opposite sign (giving a negative product) for the force to be attractive 
- so the closer (smaller r) the larger NEGATIVE value you have - the 
lower the energy level.

Does that help at all?

Best wishes

Keith



On 12/11/2013 18:21, Paul Lulai wrote:
> How do I reconcile this with U=kqq/r ?
> Isn't r getting smaller as they approach and bond?  Then U is getting larger.
>
> What is wrong with my model here?
>
> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Dr Keith S Taber
> Sent: Tuesday, November 12, 2013 11:56 AM
> To: Phys-L@Phys-L.org
> Subject: Re: [Phys-L] Energy & Bonds
>
> Hi Paul
>
> In your terms
>
> The products are more bound because they must be more bound and have LESS potential energy
>
> i.e. they require more energy to disrupt the bonds as there is stronger binding
>
> Best wishes
>
> Keith
>
>
> On 12/11/2013 15:01, Paul Lulai wrote:
> > Hi.
> > I am more aware of my conceptual shortcomings after the conversation about energy, reactions, and misconceptions.
> > I would appreciate clarification from the group on:
> > How do we reconcile the traditional Exothermic & Endothermic graphs of Energy vs reaction process with the fact that the products must be more bound and have greater potential energy? Typically the endo / exo graphs show (for an exothermic reaction) that the reactants have more energy than the products.
> >
> > I may have more follow up questions.
> > Thanks.
> > Paul.
> > _______________________________________________
> > Forum for Physics Educators
> > Phys-l@phys-l.org
> > http://www.phys-l.org/mailman/listinfo/phys-l


--


Dr. Keith S. Taber
Chair: Science, Technology & Mathematics Education Academic Group
University Reader in Science Education
University of Cambridge Faculty of Education


Editor: Chemistry Education Research and Practice
(Published by the Royal Society of Chemistry)
http://www.rsc.org/publishing/journals/rp/about.asp


Book Reviews Editor: Studies in Science Education
http://www.tandf.co.uk/journals/titles/03057267.asp



http://www.educ.cam.ac.uk/staff/taber.html

https://camtools.cam.ac.uk/access/wiki/site/~kst24/index.html



Science Education Centre
University of Cambridge Faculty of Education
184 Hills Road
Cambridge CB2 8PQ
United Kingdom


ECLIPSE -
Exploring Conceptual Learning, Integration and Progression
in Science Education
https://camtools.cam.ac.uk/wiki/eclipse/Eclipse.html