Re: [Phys-l] Mass and Energy (Binding)

["R. McDermott" <rmcder@peoplepc.com>]

----- Original Message ----- 
From: "John M Clement" <clement@hal-pc.org>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Thursday, May 25, 2006 12:39 PM
Subject: Re: [Phys-l] Mass and Energy (Binding)


> There are many issues here with respect to student understanding.
>
> There are some books which actually state that bonds store energy, so
> one must be aware of these.  In addition some teacher repeat this so
> that students may have actually been taught the misconception.
> Actually there are a large number of teachers who have the
> misconception.  Some treat this statement as shorthand for what is
> really going on.
<snip>
> So confronting this misconception requires a lot of attention to
> detail.  Yes, lots of graphs can be helpful, if students actually
> understand graphs.  This of course depends on the student audience.
> Elementary school teachers will require a different treatment from
> physics students.  But it is valuable because students can graduate
> from college with a degree in biology and still have this
> misconception.  I daresay the majority of batchelor's degree students
> in biology may have this misconception.  I was told by one that the
> college biology books even repeat this misconception.

The problem is that biology texts tend to confuse the net energy of a series 
of reactions with the energy involved in the separate steps of the series. 
In reaction kinetics, special attention is paid to the absorption of energy 
in the formation of the activated complex (activation energy) followed by 
the release of energy as new bonds are formed.  The net result can be an 
overall release of energy (exothermic - when release in the second stage 
exceeds the absorption of the first stage), or an overall absorption of 
energy (exothermic - if the release is less than the absorption).  In 
photosynthesis, the texts skip over the energetics of the multiple steps and 
focus instead on the overall release of energy "when the bonds are broken". 
Very poor pedogogically.