|Energy dispersal can be delayed for microseconds to millennia
or eons by barriers that are described in chemistry texts or are obvious.
Objects that are high above ground level have potential energy. The second
law predicts that they tend to disperse that energy by falling to ground
level. Obviously, mountains do not rapidly carry out this prediction of the
second law. No change occurs in high mountain stone until external energy
sources such as extremely violent windstorms or many freezing and thawing
cycles first physically break or crack rock portions and pieces of the mountain
so that they can disperse their potential energy by falling to lower levels.
|We humans devise all sorts of methods for obstructing or "damming"
the second law for considerable periods of time. Painting is effective
in this way not for any sophisticated chemistry but simply because it keeps
the oxygen away from iron so reaction can't occur. Chrome plating of
steel and anodizing of aluminum are other methods of hindering the second
law by interfering with the oxidation of steel and aluminum to form their
less energy-containing oxides. A Thermos bottle for hot or cold liquids
is a simple example of obstructing the rapid dissipation of heat that is
predicted by the second law.
|Some systems spread out their energy rapidly, e.g., the thermal energy
in hot objects to a cooler room, as we have been discussing. However, some
disperse their energy very slowly, e.g., the potential energy of the mass
of ice in a glacier as it moves downward over centuries. The energy
within cellulose and other chemical substances in trees, surrounded by the
oxygen in air, remains unchanged for years or centuries, but in a short while
hot flames can start the release of that energy in the form of heat and carbon
dioxide and water -- and the amount of energy released can be enough to spread
a forest fire.
|Chemical bonds are the forces that hold atoms together in a molecule.
Most bonds between atoms in molecules are quite strong; it usually takes
a great deal of energy to break them. (Conversely, when bonds are
formed between individual atoms to yield a molecule, much energy
is usually evolved.)
|In a chemical reaction, say of hydrogen with oxygen to produce water
(H-H and O-O yielding H-O-H), the bonds between hydrogen atoms in two molecules
and that between oxygen atoms must be broken and new bonds between hydrogen
and oxygen must be formed to yield two molecules of water. The breaking of
bonds and the forming of new ones occur almost simultaneously when rapidly
moving hydrogen and oxygen collide with one another -- almost simultaneously
but not quite!
|This is why most reactions require a relatively small energy "push"
to start. For example, a spark has to be introduced into a mixture of hydrogen
and oxygen before the reaction begins to form water, but then immediately
it becomes an explosion. Why this strange combination of molecular recalcitrance
followed by fantastically rapid reaction? Breaking the old bonds (requiring
energy) normally must occur slightly before the formation of new ones
(evolving energy). Thus, even though water has lower energy in its bonds
than hydrogen plus oxygen in theirs so that a large amount of energy is evolved
overall when a reaction occurs, none of that energy can be released without
an initial "push" to aid the break of a few hydrogen and oxygen bonds just
before they form a few water molecules. Once that "push" occurs, the energy
evolved as the water is formed feeds back to make many of the unreacted hydrogen
and oxygen molecules move far more rapidly and collide forcefully so they
react to evolve more energy and so on and on.
|The "push" described in the preceding paragraph is what chemists
call an activation energy. Most spontaneous reactions require this
initial input of a small amount of energy, activation energy, to aid the
first few molecules to react so they feed back their evolved energy to serve
as activation energy for succeeding molecules to repeat the cycle.
|It is this "minor" detail of chemical reactions, the activation energy,
that obstructs the instant carrying out of second law predictions and thus
protects our bodily biochemicals and our degradable artifacts from instant
oxidation and other deleterious reactions.