Energy is
defined as the ability to do work which is a really useful
definition…in physics. In chemistry it is better to think of energy
in terms of what it can do. Energy is something that can change
matter, but isn’t matter. Changing matter can be as simple as
changing it’s shape (think of molding clay), it’s appearance
(dissolving salt in water), or changing what it is (burning wood to
produce carbon dioxide and water).
Energy comes in two flavors, Kinetic
Energy and Potential Energy. Kinetic Energy is energy
associated with motion. This form of energy is the reason that a
speeding car can change the matter of a fence or tree if it leaves
the road.
A special form of kinetic energy is
called heat. This is kinetic energy when the things moving are
too small to see. In other words when a baseball is thrown at a wall
it has kinetic energy. After the baseball hits the wall, the
invisible vibrations it created in the wall when it hit are heat.
Potential Energy is energy that
is not associated with motion. It is common to think of potential
energy as stored energy, but this is not a terrible helpful
idea. In chemistry, it is better to think of Potential energy as
energy associated with position. Imagine a cartoon character who has
just run off the edge of cliff. They will certainly change their own
matter and the matter of the ground when they fall, but in the
cartoon moment before they realize that they are about to fall, they
do not yet have kinetic energy because they are not yet falling.
Conservation of energy is the
idea that energy is never lost. In other words, energy can be
transferred from one thing to another or from one type to another but
never goes away. When our cartoon character falls from the cliff he
falls faster and faster (gaining kinetic energy) while getting closer
and closer to the ground (losing potential energy). When he hits the
ground and stops, the energy is still not lost (even though he cannot
fall further and is no longer moving). At that point the energy is
transferred to the ground as vibrations that spread out until they
are so small that they can no longer be felt (heat).
The character has potential energy
because they are attracted to the earth and they are not currently on
it. These are the two pieces needed—an attractive force and
a distance separating the attracted things—for potential energy.
Thus anything that is in a position to fall has potential energy and
the further it would need to fall to reach the earth, the more
potential energy it has. In chemistry, the potential energy we focus
on is not created by gravity, but rather by charge.
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