Re: [Phys-L] Energy & Bonds

["John Clement" <clement@hal-pc.org>]

Now I understand the question better.  Of course we need to see some of the
graphs to decide.

But it may be that there is convoluted wording, or the graph may be shown up
side down with respect to potential energy.  If it is up side down the scale
labels might be confusing, even when correct.  It is like the terms energy
of fusion and energy of evaporation.  When you fuse you get energy, but when
you evaporate you have to put in energy into the reaction, but you are
expected to know what the sign is according to the process.  In other words
the graphs may be correct if you know the context.  There is a preference
for expressing things as positive numbers and students dislike/misunderstand
negative quantities so the texts may be trying to get around this, but in
the process sowing more misconceptions.

It is like the formulation of energy balance in thermo.  You have Q, W, so
what does postive or negative mean?  There are different formulations
depending on the author and the science.  Positive does not always mean
energy output (or input)!

As to the term binding energy, yes, perhaps it should be unbinding energy,
but what if you think of it as energy output?  If you made the table with
negative number the students would also be confused.  But I am very sure
that breaking bonds should be stretching bonds, which gives a better
picture.  Unfortunately these are already fixed in the literature and it is
doubtful they can be changed.  But one can change them in your class and
point out the standard words, and how they are misleading.  Notice how we
are stuck with + current flow because of Dr. Ben Franklin, but really
electrons flow, except in solutions and other odd places.  This also causes
problems.  Incidentally Ben had an honorary degree from Oxford, as I recall,
for his work in science.

John M. Clement
Houston, TX

> 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.