Law of Thermodynamics
A special thanks to:
Frank L. Lambert, Professor Emeritus (Chemistry)
Occidental College, Los Angeles
for his permission to reproduce this work.
The Second Law of Thermodynamics -- what a forbidding group of words! However, any fear of the phrase or what lies behind it disappears when we realize that we already know the second law well from our everyday experience. We just haven't recognized that such varied happenings as the following are all examples of the second law: hot pans cool; water spontaneously flows down Niagara Falls; tires under high pressure blow out forcefully if their walls are damaged; if gasoline is mixed with air in a car's cylinders, it explodes when a spark is introduced. How are all these different events described by just one law, especially a law with a complicated name?
In a hot metal pan the atoms are very rapidly vibrating (because heat has been dispersed to them from a hotter flame). They will disperse their energy to any less rapidly moving molecules -- to those in a cool counter top or those in the atmosphere of a cool room. Molecules of water atop Niagara Falls have relatively great potential energy; they disperse it if they fall far down to the river below. Molecules of air (that is composed of nitrogen and oxygen) in a pressurized tire on a car have great potential energy because those molecules were forced close together by air dispersed from a higher pressure source. The air molecules in the tire will spontaneously (and vigorously!) spread out their energy to the atmosphere if the tire is punctured or the tread separates from the walls.
|Molecules of gasoline with oxygen (from air) have greater energy
in the internal bonds that hold their atoms together than do the carbon dioxide
and water that gasoline forms when it reacts with oxygen. Therefore, gas
and oxygen spontaneously tend to react and make carbon dioxide and
water because then energy would be dispersed in the process. However, just
as compressed air in a tire is physically blocked from dispersing its potential
energy to the atmosphere by the strong tire walls and tread, gasoline and
air are chemically blocked from dispersing their energy by a barrier called
an activation energy. Thus, gasoline and the oxygen of air can
remain unchanged for years and centuries. Nevertheless, given a spark to
overcome the activation energy blocking the reaction, gasoline and oxygen
will violently react to spread out large quantities of heat from their bonds
while forming lower-energy carbon dioxide and water.
| All of the minute particles,
the atoms and molecules, in these examples will spread out their energy if
they possibly can. The second law of thermodynamics is merely the summary
of all the preceding statements that have a single theme: energy disperses
if it is not hindered from doing so. Always. This generality is far more extensive
than those five examples. All spontaneous happenings in the material world
(those that occur by themselves without outside pushing or help, except perhaps
for a spark to start, or an initial shock [that starts nitroglycerin exploding])
are examples of the second law because they involve energy dispersing.
Energy that is in the rapidly moving, ceaselessly colliding minute particles
of matter (many kinds of which, like gasoline with oxygen, contain higher-energy
bonds within them than their possible products) will diffuse, disperse, dissipate
if there is some way for that to occur without hindrance.
|The second law of thermodynamics is so much a part of our everyday
experience that it is adequately summarized in the simple examples we have
seen, the two archetypes being:
"hot pans cool down", the case of an immediate dissipation of energy,
or "gasoline explodes", the case of an obstructed dissipation of energy,because they tend to disperse the energy of their fast moving particles [that we commonly call heat] in their metal or glass to anything they contact, such as the cooler room air [slower moving molecules that then increase their speed somewhat],
because it tends to react with the oxygen in air, but does so only if the mixture is ignited. Then, the gasoline and oxygen can spread out some of the energy in their bonds (chemical bonds hold atoms together in molecules) in forming carbon dioxide and water that have lesser energy in their bonds -- but the rest of the energy is dispersed to all the molecules in the gaseous vapor (left-over oxygen, nitrogen, carbon dioxide, CO, etc.). This makes them move extremely fast (characteristic of the molecules/atoms in anything that is very hot) and the pressure in a confined space immediately increases. Such a high pressure in the small cylinder volume, amounting to a very large potential energy, further dissipates (second law again) by pushing the car's pistons down forcefully and they disperse their kinetic energy by turning the crankshaft…etc., etc.
|The word "tends" in the foregoing cannot be overemphasized. It is
omission of "tends" or "tendency" and their implications that leads most
non-scientists astray in their reading or writing about the second law. So
much stress is usually placed on the inevitability of dire effects of the
second law (and its supposed complexity) that it seems immediately threatening
to almost every aspect of our lives.
|The second law of thermodynamics is by no means an instantaneously
obeyed edict. Admittedly, it accurately predicts the probability of
the dispersal of energy that is localized or "concentrated" in a group of
molecules or atoms -- and that can result in undesirable events ranging from
serious accidents to disastrous forest fires or to our ultimate death. In
this sense, the second law is our "baddest bad". However, the law is completely
silent about two factors, namely:
(1) what will allow the second law's prediction of energy dispersal to be carried out (because many natural processes cannot occur as rapidly as a hot pan cooling down; gasoline plus oxygen or a tree plus oxygen cannot start to react without a spark or hot flames to activate them to begin their oxidation (burning) and thereby disperse part of their internal bond energy);