Re: [Phys-L] Energy & Bonds

[rjensen@ualberta.ca]

> To me what makes this diagram
> http://bit.ly/184Ow3E
> confusing is the position of the horizontal axis of the graph.  It suggests that the 0 of energy is below the curve.  I recognize that the energy in question is only defined up to an additive constant, but I see no point in implying a zero of energy that confuses the issue.  The system is bound both before and after so it makes more sense to depict the energy as being negative for both the reactants and the products.  In fact, I would move the horizontal axis to a position above the entire curve, perhaps tangent to the curve at the top of the curve.  Then the whole thing makes sense.  The reactants are strongly bound.  We add some energy to raise the energy of the particles to about zero and then some energy (less energy than the amount originally added) is given off as they drop down to a weakly bound state.

Huh? Just because a line is drawn doesn't mean it represents zero! 
This is a limitation of your understanding that needs to be corrected.

To complicate matters. The molecule does not have the energy depicted
by the line on the graph. The line represents the minimum potential
energy between reactants and products. Kinetic energy is not shown
directly. Neither is the true hypersurface with 3N-6 coordinates.
(3N-5 for diatomic interactions.)

 Dr. Roy Jensen
(==========)-----------------------------------------¤
 Lecturer, Chemistry
 E5-33F, University of Alberta
 780.248.1808