|FAQs About Entropy|
|Q. What is entropy? How is it related to the second law?
A. Entropy is not a complicated concept qualitatively. Most certainly, entropy is not disorder nor a measure of chaos! Entropy measures how much energy is dispersed in a particular process (at a specific temperature).
|Q: So, what IS the second law of thermodynamics? Well, wait
a minute, what's the first law?
A: The first law is very simple. You can't create or destroy energy.
You can just change it from one form to another, for example, electricity to heat, heat that will boil water and make steam, hot steam to push a piston (mechanical energy) or turn a turbine that makes electricity which can be changed to light (in a light bulb) or, using only a tiny quantity changed to sound in an audio speaker system, and so forth.
The second law of thermodynamics looks mathematically simple but it has so many subtle and complex implications that it makes most chem majors sweat a lot before (and after) they graduate. Fortunately its practical,down-to-earth applications are easy and crystal clear. These are what we'll talk about. From them we'll get to very sophisticated conclusions about how material substances and objects affect our lives.
Looking at the direction of energy flow in any happening/process/event is the first step to understanding what the second law of thermodynamics is and what it applies to.
Energy spontaneously tends to flow only from being concentrated in one place to becoming diffused or dispersed and spread out.
The perfect illustration is: A hot frying pan cools down
when it is taken off the kitchen stove.
|Q. Come on. All this build up for that dumb example?
A: I could have snowed you with differential equations and diagrams instead of that. We're being practical and visual rather than going the math route, essential as that is in chemistry.
The big deal is that all types of energy behave
like the energy in that hot pan unless somehow they are hindered from spreading
out. They tend not to stay concentrated; they flow toward becoming dispersed
-- like electricity in a battery or a power line or lightning, wind from
a high pressure weather system or air compressed in a tire, all heated objects,
loud sounds, water or boulders that are high up on a mountain, your car's
kinetic energy when you take your foot off the gas. All these different kinds
of energy spread out if they can. The reason for their occurring is the same,
the tendency for concentrated energy not to stay localized, to disperse if
it has a chance and isn't hindered somehow. The direction of energy
flow is just a tip of the iceberg of that law.
A. Come on now. You know that's just a figure of speech to give a feeling for the size of this principle. But... OK, let's get literal: Run that Titanic movie as the ship hits the iceberg. See those steel plates ripped open and the ship begin to sink. Realistic, right? Can you imagine a real happening in which the reverse occurs? A sinking ship whose steel side heals up as it comes up out of the water and floats? Ridiculous. Too stupid to think about. But why is it stupid? Because it is so improbable from your and my experience. Only a movie run backward would show that kind of unrealistic fantasy. The second law isn't some weird scientific idea. It fits with everything common happening that we know.
Our psychological sense of time is based on the second law. It summarizes what we have seen, what we have experienced, what we think will happen.
Sinking ships are like rocks rolling down a mountain -- as they sink, their potential energy due to being high above sea-bottom is diffused, spread out to the water that they push aside (or, in the case of mountain rocks, diffused as they roll down to the valley and hit other rocks, give them a bit of kinetic energy, and warm them slightly by friction.)
In a video that is run backward, you may have laughed at some diver who zooms up from the water to a ten-meter diving board, but you're never fooled that the video is going forward, i.e., that you are seeing an event as it actually happened in real time. Unconsciously, you are mentally comparing what you see now with your past practical experience -- and that has all followed the second law. Even though you may never have heard of the law before, in the years of your everyday experience you have seen thousands and thousands of examples of energy flowing from being concentrated to becoming diffused.
A swimmer doesn't come shooting up out of the
water to the diving board, rocks in a valley don't
|Q: You mentioned those tricky words, "spontaneously" and "tends"?
A: In the second law "spontaneously" means only that any energy which is available in the object or substance for diffusing will spread out from it -- if given a chance. It doesn't have anything to do with how fast or slow that occurs after the dispersal of energy starts, or even when it might start. That's why "tends" is so important to understand as part of the second law.
The energy available in a hot frying pan or
in a loud BOOM from a drum immediately and rapidly begins to spread out to
their environments. Nothing hinders them from happening. Lots of unhappy events
are like that. But there are an enormous number of "energy diffusing" second-law
happenings that are hindered so they don't occur right away. Here's a simple
illustration: If I hold a half-pound rock in my fingers so it is ready to
fall, it has potential energy concentrated in it because it is up above the
ground. If the second law is so great and powerful, why doesn't
the energy that has been concentrated in the rock spread out? Obviously,
it can't do that because my fingers are "bonding" to it, keeping it from
falling. The second law isn't violated. That rock tends to fall and diffuse
its energy to the air and to the ground as it hits -- and it will do so spontaneously
by itself, without any help -- the second I open my fingers and "unbond"
|Q: Is this understanding of "tends" really so important?
A: Yes, it is. Many philosophers and novelists learned about the second law only from physicists. The writers pass too quickly over the fact that it is a tendency rather than a prediction of what will happen right away.
In many real-world chemicals and things the second law can be obstructed or hindered for millions of years. Certainly, the mountains of the world haven't all slid down to sea level in the last several hundred centuries! Similar to my fingers holding the small rock (but millions of times more tightly), even overhanging stone in cliffs or mountains is bonded, chemically bonded, to adjacent atoms of stone and so the stone can't obey the second law tendency for it to fall to a lower level. Here, as in countless other examples, the second law is blocked by chemical bonds. It takes a huge number of repetitions of outside energy input like freezing and thawing and earthquakes and windy rainstorms to break the bonds along a weak bond-line, make a crack, and free particles or pebbles or rocks so they can follow the second law by falling to a lower level.
Blockage of the second law is absolutely necessary
for us to be alive and happy. Not one of the complex chemical substances
in our body and few in the things we enjoy would exist for a microsecond
if the second law wasn't obstructed. Its tendency is never eliminated but,
fortunately for us, there are a huge number of compounds in which it is blocked
for our lifetimes and longer.
|Q Isn't it about time we got to something human rather then rocks?
A: Chem profs approach the second law the other way around, starting with atoms and molecules first. Professors rightfully avoid much talk about the behavior of big visible things at all. In the limited time of a chemistry course they can only develop the nature of atoms and molecules and of chemical substances. Objects made from chemicals like a gear or a bridge or a wooden house or a book or a bone just have to be assumed to behave like their constituent substances.
Wood and paper are both primarily cellulose. Paper is easier to experiment with so let's think about its burning. When paper catches fire and burns, there's a lot of energy given out as heat and some as yellow light. It's well known now that the products of the combustion of cellulose with the oxygen of the air are carbon dioxide and water. (The slight amount of black ash is due to the clay that was on the paper adsorbing a small amount of carbon.) Once started, the burning is spontaneous --i.e., the process goes on by itself without any further help after a match starts it -- and also burning is really fast. Now, if energy is flowing out in this reaction of paper with oxygen, the paper and oxygen must have had a lot more energy inside them before the reaction than do the carbon dioxide and water after the reaction .
What's happening here is a beautiful illustration
of the predictions of the second law. Systems (groups) of chemicals -- or
objects made from them (like sheets of paper or houses) -- tend to react
if they have more energy bound inside their molecules than do the reaction
products that they can form. Then, when they react, they are spontaneously
spreading out their internal energy in two ways: 1) only a part to each molecule
of the products because each has lesser energy concentrated in it than was
in the starting materials, and 2) giving those product molecules much more
kinetic energy (making them move much faster) than the original cellulose
and oxygen. These fast molecules show a high temperature on a thermometer;
we say they are hot, not because heat is a "something" but because heat is
the process of energy transfer from one kind of matter to another -- from
fast molecules of gas to the thermometer bulb or to one's hand if you're
so foolish as to put it in a flame.
|Q: You had to put a match to that paper to start it burning!
What's spontaneous or second law about that??
A: Have you already forgotten that essential word "tends" in the second law?
All the paper and wood and things made from them in the entire world tend right now to react with the oxygen in the air and form one gigantic fireball. Why don't they? Well, why don't all the mountains on earth spread out the potential energy in their high stone cliffs this second and collapse into spread out much-lower mounds of sandy particles? It's the strength of the chemical bonds (between silicon, oxygen, potassium, aluminum and other atoms and ions) that holds stone together and acts as an obstacle to the second law's immediate execution. The potential energy of high rocks/mountains is hindered from spreading out instantly.
Just so, the strength of the chemical bonds (between carbon, hydrogen and oxygen) in cellulose holds it together and obstructs the instant spreading out of the energy inside the cellulose in air. This strength prevents oxygen from instantly breaking into the cellulose molecules to form even stronger bonds (of carbon dioxide and water) and to release large amounts of energy (because the stronger the chemical bond, the less energy is contained within the molecule). However, it takes just a little extra push of energy from the match flame to start to break a few sextillion bonds in the cellulose of paper or wood.
The initial energy push (usually from heat), the small energy
"hill" in the diagram below, is the activation energy, Ea, that is necessary
to overcome the bond-strength obstacle to the second law in most chemical
reactions. Thus, this requirement for input of an initial energy, the energy
of activation, hinders both desirable and undesirable reactions from occurring.
As these first "heated up" bonds are breaking, the oxygen from
the air begins to grab carbon and hydrogen atoms to form carbon dioxide and
water molecules. But the formation of new strong bonds in the CO2
and water gives out a lot of energy -- enough to start to break many many
more sextillions of bonds of cellulose (no bond being totally broken before
oxygen has simultaneously begun to form a new CO2 and water molecule
from the developing fragments). These new molecules of CO2 and
water also absorb some of the energy from the new bonds as they are formed
and many move faster than twice the speed of sound. We sense
those fast moving molecules as hot gas and we call it "heat".
|Q. I remember that in the Malibu fires a couple of years
ago some houses started to blaze from the inside because heat from the nearby
burning trees and brush ignited the cloth drapes inside the picture windows.
Then there were others with big windows that didn't catch fire because they
had aluminum blinds which were closed. That involved activation energy, right?
Cotton cloth is cellulose, isn't it?
A. Yes to both questions. First of all, the glass of the windows probably got extremely hot, both from the heated air of the fire and the fire's infrared radiation. In addition, as you suggest, the intense IR radiation went right through the windows and heated the fabric drapes even more -- enough to exceed their activation energy that normally hinders their oxidation in air. They began to burn and this gave out enough energy to ignite the whole interior -- by exceeding the activation energy of oxidation of all the other flammable materials in the house.
Just as does every idea that we've been talking about, the concept of activation energies gives us tremendous power in understanding how the world works, even in unusual events. For instance, you've heard about the dangers of nitroglycerin, a liquid that explodes violently just from being shaken hard or jarred sharply. Do you think that its energy diagram would look like the one for cellulose above? Of course not. It must have a very low activation energy, Ea. That leads to an extremely fast formation of hot gaseous products, an explosion (despite the relatively small difference in energy between "nitro" and the products). Explosives form hot gases so rapidly because they all have oxygen atoms as part of their molecules. Thus, they are not limited in their reaction rate by access to atmospheric oxygen as are most substances. Alfred Nobel was driven to invent a safer explosive when four workers and his brother were killed in the family nitroglycerin plant. He made what he called "dynamite" when he mixed oily nitroglycerin with some powdery silica material to form a seemingly dry solid that could be pressed into stick shape. They didn't detonate just from being hit or dropped. Obviously, therefore, a considerably higher Ea indicating that more energy must be put in, e.g., by a blasting cap, to initiate the spontaneous decomposition of the nitroglycerin. (TNT, used in armor piercing shells, is about six times more resistant to shock than nitroglycerin. Thus, you can guess at TNT's activation energy for reaction.) Dynamite has been mainly replaced by other explosives for excavation, etc., today.
There. We've seen some substances with low
activation energies but we don't often run into nitro or TNT!
|Q: What about the flow of enegy? and the waste from this energy
A. Nature's second law predicts that the energy concentrated inside a chemical like oil or coal (or food) will spread out. It will, if the proper other chemical (usually oxygen) and if that necessary little energy push to overcome an activation energy barrier are also present. We make our whole technological world run by grabbing as much as we can of the energy flow available from concentrated energy sources like fuels to run an infinite variety of machines, electrical generators and vehicles. (Our bodies, as we have said, use second-law energy flow from the oxidation of food for the synthesis of essential compounds and for all activity, from biochemical to muscular to mental.) However, when we change energy from one form to another it is impossible for us to get to use all of the energy in the concentrated energy source for the jobs we want it to do. Some always must be wasted, mainly as unusable heat to the environment, a sort of necessary 'energy friction' in every real-world energy transfer. That's where our body gets heat to maintain our 37.0ºC.
This fact of some unavailable, unusable energy
when it is transferred is really a hint about the ultimate basis of the scientific
statement of the second law -- of what can be considered the ultimate cause
for energy to flow in one direction only. I have avoided mentioning it until
now because it is very abstract compared to its practical, down-to-earth
results of lightning, explosions, engines running and flat tires. It's entropy.
|Q: Are you serious?
A: Let's look at the mining of iron ore. It's scattered all over the earth, sometimes in big pockets that are very valuable because they have an especially large concentration of iron oxide.
This minute all around the world there are tens of thousands of people who are "using" (transforming to mechanical work, losing some to waste heat spread to the environment) the concentrated energy in coal, oil and gas to dig up the ore with giant scoops and transport it via trucks, trains, and ships from different mines to steel mills. Then, more energy is used by more thousands of people to change it into iron and finally to shiny steel...What a long parade of actions based on using the second law to get what we want!
Every step from the original rusty dirt in the ground requires
transformation of concentrated energy (in coal, oil, gas) to do a lot of mechanical
work (along with that dispersing of less concentrated energy in the hot exhaust
gases of CO2 and water). Then bringing together thousands and
thousands of tons of ore, coal and limestone to one place, the steel mill,
is another enormous expenditure of concentrated energy in fuels (not counting
the human effort in muscle and brain). Next, a totally different variety
of energy transformation is done, changing the iron (oxide) ore to iron metal
that has a larger internal energy content in its bonds that does the oxide.
Wait a minute! Doesn't it seem against the second law to force a dispersed-energy
chemical like iron oxide to change into a concentrated-energy chemical like
nearly pure iron? Sure it is, but there's no problem -- if we are willing
to pay the second-law price of loss of some of the energy as wasted heat.
Just as in running all those truck, train and ship engines, we can take energy
flow from a spontaneous process (here in this case, from two chemical processes):
Did we beat the second law? No way. But by
using the second law (taking the energy from two spontaneous "downhill" reactions
and transferring much of it to force a nonspontaneous process to go "uphill"
energy-wise and make something), just as we take gasoline energy and change
some of its energy into mechanical energy (to make nonspontaneous engines
turn the car wheels), we got what wanted: iron from which we can produce
steel, the structural material for a near-infinite number of useful objects.
|Q: Are there more examples?
A: Lot's of them. Let’s finish this recap of human use of the second-law energy flow: Besides making concentrated-energy chemicals like iron, copper, chromium and silver from their diffused-energy ores, we make thousands of other high energy substances for our pleasure or our needs. Minor things like flavors for foods. Important pharmaceuticals that save millions of lives. It may take dozens of reactions (milder than that violent one for iron from iron oxide!) to change starting materials stepwise to the final chemical product, but the overall process involves diverting energy from spontaneous reactions to make the substance we want.
Of course, this is the kind of coupled process (i.e., a spontaneous
+ a non-spontaneous) that nature uses – taking a tiny bit of sunlight energy
and, with the aid of extremely complex processes in organisms like plants,
changing lower-energy carbon dioxide and water and traces of minerals into
thousands of higher-energy substances. But don’t think that "natural" or
"from natural materials" has something to do with good or harmless! There
are hundreds of harmful or even poisonous chemicals in nature – from strychnine
to the extremely deadly compound in simple castor beans. Also usually omitted
when someone extols the beneficial qualities of everything "natural" is the
fact that all terribly toxic viruses and bacteria are totally natural!
|Q: You're using doublespeak on me! First you said it was bod for
us and now you show that the second law is a good buddy because we can use
it to get energy to do what we want. What's the story?
A: You're not naive so stop acting like it. . Life is full of stuff that can be good and bad. But stand back now:
The second law is the biggest good and the biggest bad on earth.
The good: Because of the second law about the
direction of energy flow, life is possible.
We can eat concentrated energy in the form of food and process that energy (using some, losing some) unconsciously for synthesizing complex biochemicals and running our organism, consciously for mental and physical labor, excreting diffused energy as body heat and lesser concentrated energy substances.
We can use concentrated energy fuels (most frequently, plus oxygen) to gather all kinds of materials from all parts of the world and, without any energetic limitation, arrange them in ways that please us. Similarly, we can effect a near-infinite variety of non-spontaneous reactions such as getting pure metals from ores, synthesizing curative drugs from simple compounds, and altering DNA.
We can make machines that make other machines, machines that mow lawns, move mountains, and go to the moon. We can make the most complex and intricate and beautiful objects imaginable to help or delight or entertain us.
Every organic chemical of the 50,000 different kinds in our bodies is metastable, synthesized by a nonspontaneous reaction and only kept from instant oxidation in air by activation energies. (Loss or even the radical decrease of just a few chemicals could mean death for us.)
When these feedback subsystems fail -- due to inadequate energy inflow, malfunction from critical errors in synthesis, the presence of toxins or competing agents such as bacteria or viruses -- dysfunction, illness, or death results: energy can no longer be processed to carry out the many reactions we need for life that are contrary to the direction predicted by the second law.
|Q: Aren't Murphy's Law and the second law related? Murphy's
Law isn't about death, just about less bad things that hit us?
A: Murph doesn't get that serious very often, but there are at least five thousand illnesses, diseases, "things that can go wrong" with our bodies that may not kill us. That's 5K of Murphs. These are biochemical problems that humans suffer from. But how many do most people have? Did you ever see a PDR Medical Dictionary or an AMA Home Med Encyclopedia? They'll make you very thankful for activation energies and feedback systems that keep your bod working as well as it does (and long as it will) to counter the second law, using food intake as your energy source.
However, let's look at the other annoyances (and disasters) that the mother of all Murphys is responsible for when things that are around us have energy concentrated inside them. That's always potential big trouble. All that has to happen, somehow, sometime, is for a little energy push -- a spark, a flame, an impact -- to get up over that activation energy hill.
First, problems caused by the thing or material having concentrated
energy inherent in its chemicals:.
And, of course, there
are many less (or equally) dramatic examples in the oxidation of metals
Second, annoyances (or worse) due to concentrated energy in the
object being present or flowing by it, but not inherent or part of its nature:
|Q: Fine. I get the point. Or points. Know too much about car
crashes. New to me, before we began to talk, was to hear that burnable stuff,
wood or paper or cloth, in my room is basically made of concentrated energy
chemicals. But I don't have sparks or candles around to give them an activation
energy kick. Breaking things is more of a problem to me. Is there energy locked
inside a skateboard or a ski that wrecks me because it tends to diffuse or
A: Good comment and good question. It's great that you now understand why certain things can react with oxygen and why a spark or low flame sets off a spontaneous reaction. You also know now that all of these kinds of problems from plane and car crashes to lightning to tornadoes and fires are related by the second law of thermodynamics: concentrated energy tends to spread out. (A fast moving car is a "reely big" bundle of concentrated kinetic energy.)
Your question about breakage is just as important because that kind of incident or accident happens to us more often than "Murphy problems" of fire from energy concentrated inside the object.
Breaking things involves concentrated energy that is initially outside the thing that gets broken. It's the second law working in the environment of the object -- energy flowing around or through it for some reason or other and hitting it with enough energy and of the right kind to tear it apart. (Right kind? Right amount? Heat won't make a concrete bridge shatter into fragments in thirty seconds, but a strong earthquake will.) Chemists never talk about breaking things because they don't consider that to be a chemical process. The chemical nature of a ski that gets broken, for example, isn't changed. It's just two skis so far as the chemicals in it are concerned. (Try to tell that to the skier.) Technically, the energy content of the two pieces of ski has not been appreciably altered so chemists call a fracture a physical process.
However, in a micro sense it is a chemical process because in any break chemical bonds are ruptured all along the line of the break as well as complexly broken and reformed near that break line. It's just that the number of bonds altered is extremely small compared to all the others in the ski that are not affected and therefore a chemist would never be able to measure any energy change. Also, where and when the break will occur depends on so many factors that aren't what chemists call fundamental, such as: how the object was made, its shape, its ratio of surface area to volume, the strains and defects present in it, whether it is brittle or ductile and even the rate of application of energy to it.
You are probably aware that microparticles continually change speeds when they collide, but they average roughly around a thousand miles an hour at ordinary temperatures. When they are in a gas, they go a little distance before colliding, not so far when as a liquid, and as a solid they can only vibrate that fast.
Fast-moving atoms and molecules incessantly run into one another,
tending to become as scattered as they can be, and in this way energy is transferred
and spread out in any way available to them. This is what entropy measures.
(That "available to them" phrase means that they may be held in place by
chemical bonds until these are broken, that they can’t magically go through
walls or to physically improbable locations, and their energy content limits
them to being in probable energetic levels, not improbably high ones, under
|Q: Watch it! That's too big a jump -- from concrete chunks to atoms
A: You're right. You're keen to sense instantly what many non-scientists miss: big pieces of matter are made of tiny particles, atoms or molecules or ions, but obviously they don't behave as does a single small particle. (More about that error in a minute.)
I jumped that way in talking with you just because those drastically broken bridge bits that once moved all around randomly allowed me to bring in entropy's relation to the atoms and molecules that are always moving to all kinds of locations "available to them". Why and how microparticles move to all positions in their available space is vital in understanding the scientific details of the second law in chemistry. But I think that it is better to keep to generalities rather than introducing too many chemical details in our talking together here.
The remainder of this section will straighten out some of the confusion that popular and scientific writers have created around the word "entropy".
Frequently, outside of chemistry, physics or
molecular biology, entropy has had its relation to its scientific roots of
heat and temperature ignored. The results are disastrous for nonscientists
trying to get a feeling for how the world works. Instead of correctly applying
entropy to the normal behavior of energetic atoms and molecules, many authors
have misled their readers by saying thermodynamic entropy explains the mixing
up of all kinds of ordinary things like books or clothes in a dorm room or
playing cards that are immobile non-energetic objects or even people's relationships.
Maybe it's stupid to say, but even though sheets of paper and books and decks
of cards often get all mixed up, they don't go flying around by themselves
like molecules in a gas.
|Q. Of course that's stupid to say. Why tell me that?
A. Because of quotations like those in the next paragraph. Don't they give you the feeling that the clutter and the messes have occurred by themselves, just like molecules spontaneously move all around randomly without any outside influences? Couldn't readers who weren't as analytical and science-minded as you begin to wonder if some weird unseen force called entropy was always lurking in the dark, ready to push things here and there and everywhere?
In a textbook there is a picture of Einstein's
desk taken the day he died with a statement, "Desktops illustrate the principle
that there is a spontaneous tendency toward disorder in the universe..."
Wow! Stay away from desktops -- you don't want to get caught by the scary
spontaneous tendency that happens there! Here's a quote and a photo that
really deceives a reader by the first four words that I've italicized: "If
left to themselves, the books and papers on the top of my desk always tend
to the most mixed-up, disordered possible state." Wasn't the writer ever
near the desk? Some mysterious alien force from outer space did it? Another,
from a book that sold over a million copies: "Anyone who has ever had to
take care of a house, or work in an office, knows that if things are left
unattended, they soon become more and more disorderly..." Unattended usually
means nobody around, doesn't it?. Isn't that writer implying that things
all by themselves cause this disorderliness, rather than people? (He should
be told that King Tutankhamen's tomb was left unattended -- really unattended
-- for 3274 years and its arrangement of things was found to be totally unchanged,
though dusty, when the tomb was finally opened in 1922.)
|Q: Why be so critical? Those writers just failed to say that they
or somebody else was messing things up. What's this got to do with entropy?
A: That's not a minor omission! It's like a guy outside a bank telling you (as police were running toward you two), "Look at all this money that the nice bank teller shoved at me" and just failed to say, "I had a gun pointed at him." Don't you think the gun had something to do with the money-shoving?
As I said a minute ago, reading statements like these in books gives many people who aren't as sophisticated as you a strange idea about entropy: it's a mysterious force that makes ordinary things jump around and is at work to mix up the world. That's nonsense. Remember that the authors are writing about the second law of thermodynamics, but using the word entropy for it (in sentences near the above quotes). In only a few minutes together by looking at examples of energy flow in the world, we have found that seeing the second law act that way is not at all mysterious. In fact, it erases all the mystery from dozens of everyday happenings.
BUT -- and I put that in capitals to warn you about the most frequent error of scientific as well as popular writers -- even texts "leave out the gun" when they start talking about the ordinary world getting mixed up and "going toward disorder". It's people who mess up desks and dorm rooms (and much of the environment), it's hurricanes and tornadoes that tear houses and trees to pieces and scatter the bits; it's earthquakes that can even fracture a concrete freeway and topple a whole building. What's common to all those examples? The flow of energy going from concentrated to dispersed, of course. As a result of that process, solid things get scattered all over and mixed up. The objects do NOT, by themselves, become disordered or random. There isn't any "tendency of objects to become disorganized" in nature any more than bank tellers have a "tendency to give money to robbers" -- without a gun. Energy flow of many kinds is the driving force, the gun, for the world's macro objects tending to become disorderly.
Whenever an adequate* amount of
energy flows through a system of objects, it tends to scatter them. (The energy
flow, if adequate*, can break bonds and disperse the resulting object parts.)
They will be strewn to random, statistically probable locations consistent
with all applicable factors of the objects and their flight paths or those
for their fragments. In this process the concentrated energy in the energy
flow becomes diffused in imparting kinetic energy to the objects; its entropy
is increased. Unless the original objects (or an appreciable part of them)
are ground into a fine powder, their energy and their entropy contents are
essentially unchanged a short while after the process of movement and scattering
has stopped. (This time period allows temporary heating effects to come to
equilibrium with the atmosphere.)
|Q: Then is this OK? Fast-moving microparticles tend toward randomness,
because they thereby can spread out any energy in the system better. Ordinary
non-moving solid objects don't tend to go anywhere by themselves (the mobile
atoms inside the objects don't make them jump around!) But if solid
things are hit from the outside by energetic winds (or people) of course
they get shoved into mixed-upness or randomness. But I'm uncomfortable
with that "No change in entropy in macro objects if they get all mixed up
A: Great summary. Here's more of the whole picture of why there is zero entropy change in shuffled cards or messed up rooms. (Zero change in cards or rooms, but there IS entropy increase in the card shuffler's muscles or the room trasher's!).
Too many writers say that the same is true of large ordinary solid things,when they talk like this: "A disorderly and mixed-up bunch of a number of solid objects has a higher entropy than those same objects in an orderly pattern." This doesn't make sense. Inside disorderly, scattered solid objects -- whose molecules aren't changing at all-- there is exactly the same number of microenergetic states for those molecules as there is in a pretty patterned arrangement of the objects. Whatever pattern the big visible objects are lined up in, it is totally external to the molecules and their behavior. So it is absurd to talk about an entropy change in a group of random solid objects versus the same ones when they were put in some neatnik pattern. NO entropy change occurs in macro objects when they are altered from ordered to disordered or vice versa. ZERO, zilch, zip, nada entropy change because the number of microenergetic states within them is completely unaffected.
Excuse me for being so repetitious but textbook authors rarely take the space to make this important point clear to students. (Just wait until you see some horrors in the next paragraph. Most books for nonscientific readers are even worse.).
A typically erroneous quote from a high school chem text is: "The law of disorder states that things move spontaneously in the direction of maximum chaos or disorder." First of all, there is no such law of disorder for things. But the worst here is how the sentence misleads students about things moving by themselves when the author puts in that word "spontaneously". That defeats understanding of how the second law works. Molecules tend to become random spontaneously by themselves, but things do NOT. Every movement toward disorder of a solid object involves an energy flow of some sort from outside it that pushes it. The entropy increase in the energy flow as it becomes more dissipated while moving the object is interesting. The zero entropy change in the object is a scientific bore.
"Scattered marbles have a higher entropy than gathered marbles." Here is another example of dozens you could see in texts and articles -- totally erroneous because it refers to big visible things rather than microparticles. Marbles aren't molecules, constantly moving at a thousand miles an hour in many different translational and rotational microstates! And, of course, the same is true of a card deck or of clothes and all the stuff in a dorm room: the shuffled deck or the new deck each has the same entropy; the messy room and the neat room likewise.
We are not talking here about human judgement of patterns or preferences
or esthetics, just about thermodynamic entropy. A sparkling and neat Martha
Stewart bedroom may look much better than the same room after a slob has
lived there a month, but the entropy change is zero -- even though that kind
of guy could be thrown out legally in less than a week. Any entropy change
that occurs when things are moved occurs in the person (or wind, or earthquake)
that messes it up.
|Q: So what?
A: So everything! This is the payoff.
People from the beginning of history have worried about material things going wrong in their lives. About why bones break, why shiny copper jewelry (valuable in antiquity) turns green, why tools wear out, why rivers of mud rush down the hills and wreck the village, why people get sick, why they die. Fate and karma and spiteful gods have been just a few of the infinity of inaccurate solutions to the threatening problem of seemingly erratic nature. "Why me?" has probably been a human feeling before the invention of language. It is common today in any catastrophe. Is it justified?
You now know the basic cause of every material/physical event that we think is bad: It is the second law or, more accurately, what the second law describes: the behavior of energy in our real world. All the structures that we prize -- from our own bones to our artifacts like chairs or houses, skyscrapers, bridges or jet planes -- are subject to being broken or destroyed by adequate energy flow moving from being concentrated to becoming spread out and diffused. The distressing results of forceful impacts on bones and cars and buildings are simply manifestations of this tendency of concentrated energy.
(Quakes and violent winds are temporary and coincidental accumulations from less concentrated energy sources).
Further, you know now that all the chemical catastrophes that hit us are similarly caused because the substances involved in the disaster obey the second law. Whether forest fire, or Hindenburg explosion, or dangerous corrosion of a car part, blocking of brain patterns by Alzheimer's factors, or bacteria that interfere with a critical feedback system in the body -- these are just examples of concentrated energy spreading out contrary to our human preferences.
As one of our major goals, we humans want order and organization of many different varieties. An equally important goal is our desire for concentrated energy substances as materials in our artifacts and as totally controllable power sources in our machines. Neither goal is consistent with the second law. Yet we are surprised when, against our naive wishes, the predictions of the law actually come about. Murphy's Law (speaking only of matter-related events) fits an emotional human need when we are frustrated; it is humorous because it is such a gigantic exaggeration.
However, we may subconsciously let its humor make us concentrate on things going wrong and blind us to the most amazing fact in our second-law world: Usually things do NOT go wrong. There are three major reasons that they don't: First, constant human care and caution in protecting against second law predictions. (Two mundane examples: actions that reduce the possibility of fire in industry and the home, painstaking design for safety and the continued careful inspection of airplanes.) Second, the existence of activation energies that obstruct and block the second law from milliseconds to millennia. Third, the literally incredible organization in living things: from simple amebas to humans, from primitive grasses to complex plants, all those energy processing systems live and procreate because they are protected from failure by an enormous variety of feedback mechanisms.
It is often the failure of only one activation energy out of billions, or one feedback loop out of thousands, that makes Murphy's Law seem valid. A fractured leg in a ski accident, a spark in the fuel tank of TWA Flight 800, a broken timing gear in a Corvette, a fire in a fraternity house started by a forgotten cigarette, a California freeway collapse in an earthquake, a fall from a horse that results in a broken spine and quadriplegia -- all these are examples of activation energies being exceeded, whether in chemical reactions or physical fractures. Together with the thousands of illnesses that can destroy our functioning as whole persons, they constitute "things going wrong" in people's lives.
But activation energies that obstruct undesirable chemical and physical events almost always protect us and our prized objects even from disastrous change that the second law predicts. Bodily feedback systems almost always protect us from bacteria and malfunctionintg human biochemistry.