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Re: [Phys-L] defining energy



To my memory, every single high school physical science and chemistry book I've seen simply state that there is, "energy stored in the bonds of the compounds" or something along those lines. It is a very easy step to the 'break a bond get your energy' egg yolk theory.
Adding to the issue, saying that something is more bound or has greater binding i think feels like there is more energy holding them together. Not that the composite atoms are in a lower energy state and more stable.

I wonder what is a good graphical way to represent this? For many energy things we introduce the concepts with energy bar charts. Perhaps it is time to try to use energy bar charts with bonding and energy? Maybe energy wells would work as well.
If, during exo and endothermic reactions, most or all reactions included bar charts for the reactants and products, would that help? Maybe endo / exo rxns include energy wells for both the reactants and products.

Is this done somewhere already?

Paul.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of jbellina
Sent: Wednesday, October 30, 2013 1:25 PM
To: Phys-L@Phys-L.org; Bruce_Sherwood@ncsu.edu
Subject: Re: [Phys-L] defining energy

This is a very important issue, and has its origins I suspect in elementary and middle school science where students learn about energy being stored in materials and transformed, so a battery is an energy source and makes the bulb light. (This also leads to a lack of understanding about complete circuits, but that is another sad tale.) It shows up again often in college biology where students are told that energy is stored in bonds and becomes available when the bonds are broken. They ignore completely that the energy is released when more stable bonds are formed with surrounding hydrogen. I call it the egg yoke theory of energy production, crack the egg and yolk comes out, crack the molecule and the energy comes out. It is how they think about it, so I am not surprised it is occurring is high school teachers as well.

It's no yolk!

joe

On Oct 30, 2013, at 12:55 PM, Bruce Sherwood wrote:

Following up on John Clement's comments about gasoline and oxygen, I
found when teaching a distance education version of Matter &
Interactions for in-service high school physics teachers that many of
them were surprised to discover that they had been carrying around a
view of binding energy that was basically backwards, with the wrong
sign. The view was something like "there is energy stored in the bonds
in the gasoline molecules which we can use" instead of "in combustion
the molecules transition to a lower energy state and become more
bound". To put it another way, they seemed to have thought that "more"
in the bonds (more binding) meant more "bond" energy was available,
instead of more bonding being associated with lower energy, not higher.

I'll admit I can't express the issue very clearly, but the teachers
themselves were convinced that useful energy resulting from
transitions to lower energy levels (greater binding) was a new idea for them.

Bruce
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Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net




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