Grandpa -
When, for example, carbon reacts with oxygen to produce carbon
dioxide and
A. D. Reichle
Sent
from AllExperts.com at 24 Sep 2000
Note:
Grandpa is listed as an expert in physics on this site.
Some of the examples come from there.
Dear A. D. -
No - this is not an atomic reaction, but a
simpler chemical reaction. The heat
comes from electrons changing the amount of what is essentially kinetic energy -
from changing the energy of their "orbits."
(They're not really orbits - but the motion of electrons is kinetic
energy.) There are other energies
in atoms and molecules - bonds, etc., which may change also during the reaction.
But also:
Yes -
If we consider that energy and mass are simply two forms of the same
thing, then the energy lost could be viewed as mass lost.
This is not quite like an atomic reaction, wherein the mass itself is
altered. In the chemical reaction,
the measured mass remains the same if we make sure we have all the product of
the reaction to measure.
This is a good question, and there is much
we don't understand. Since energy
is "given off" in this reaction, some of the kinetic energy internal
in the molecules (atoms) is converted to kinetic energy of the motion of
surrounding molecules (heat). This
is called an exothermic reaction - one in which heat is given off during the
reaction.
There are other chemical reactions that
"take on" energy rather than giving it off.
We call these endothermic reactions.
An example is the reaction required to
separate oxygen and hydrogen in water. This
is endothermic. We put energy in to
cause the reaction. We can do this
by causing an electric current to flow through the water.
Oxygen will collect at one electrode and hydrogen at the other.
Now we may put the oxygen and hydrogen back together to get water - this
is exothermic - it gives off energy. In
fact, it's an explosion. Just mix
hydrogen gas and oxygen gas and light it - bang.
The only "waste" product is water.
What a great way to run an engine - if we could obtain hydrogen gas
cheaply enough. If we obtained the
hydrogen by separating the oxygen and hydrogen in water, it would take more
energy to obtain the hydrogen than the burning of it could give us back.
Keep thinking this way.
- Grandpa