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Thermodynamics

How important are the laws of thermodynamics?

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?

– C. P. Snow, 1959 Rede Lecture, “The Two Cultures and the Scientific Revolution”.

Thermodynamics

from the Greek θερμη, therme, “heat” and δυναμις, dynamis, “power”.

the study of the conversion of heat energy into other forms of energy, and vice-versa.

Thermodynamics is not based on studying one particle at a time. Rather, it is based on statistics: studying the collective motion of millions of particles.

It’s essential for physics, chemistry, chemical engineering, aerospace engineering, mechanical engineering, cell biology, biomedical engineering, materials science, and economics to name a few.  (Wikipedia)

The laws

British scientist Charles Percy Snow summarized the laws as:

1. You cannot win (you can’t get something for nothing, because matter and energy are conserved).

2. You can’t break even (you can’t return to the same energy state, because there is always an increase in disorder: entropy always increases).

3. You can’t get out of the game (because getting down to absolute zero is unattainable).

This infographic describes the laws in a different – but equivalent – way.

(notice that there is a Zero-th law that isn’t listed in C. P. Snow’s playful summary)
thermodynamics-laws-birds
Now let’s look at each of these laws in more detail:

Zeroth law of thermodynamics

This law is so simply, most people assume that it’s true, and don’t even mention. But for the sake of completeness, we include it:

Zeroth law is like the transitive rule of algebra

If A = B  and B = C  then A = C

If temp of object A = temp of object B,
and temp of object B = temp of object C,
then temp of object A = temp of object C

So all three systems would be in thermal equilibrium

Let’s watch three different materials fulfill this law, by coming into thermal equilibrium. Animation by Charles Xie

Thermal equilibrium (in this example) is reached when the temp of all pieces = 13.4 degrees C.

zerothlawthemo

http://weelookang.blogspot.sg/2012/09/the-zeroth-law-of-thermodynamics.html

Also see https://www.grc.nasa.gov/www/k-12/airplane/thermo0.html

Another way to view this:

“When body A is placed in thermal contact with body B, there will be a flow of thermal energy between the two bodies.
Thermal energy will flow from the body at a higher temperature,
to the one at a lower temperature,
until thermal equilibrium between the two bodies is reached.”
– Loo Kang Lawrence

Charles Xie Thermal Equilibrium
_____________________________________

First law of thermodynamics

1. You cannot win (you can’t get something for nothing, because matter and energy are conserved).

If heat is lost from one system, that heat goes someplace else. It can be turned into work, or it can heat something up.

The first law applies to any machine, and even to any living organism

Notice that no thermal energy is ever “lost”; it also must go somewhere.

 

also phrased as

2. You can’t break even (you can’t return to the same energy state, because there is always an increase in disorder: entropy always increases).

OR

Heat will not flow spontaneously from a cold object to a hot object

OR

You cannot create a heat engine – which extracts heat, and converts it all to useful work.

Second law thermodynamics waterfall

2nd law

image from http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html

The second law is observed in different ways:

Heat engine

Refrigerator

Entropy

Heat transfer

___________

The second law is related to entropy

Great… what is entropy?

entropy is the amount of disorder (in a gas, a liquid, objects in a room, etc)

second-law-of-thermodynamics-entropy

 

Entropy really measures the dispersal of energy: how much energy is spread out in a particular process

We know from everyday experience how energy spreads out – and how it doesn’t. This ice melting looks normal.

melting-icecubes-gif

commons.wikimedia.org/wiki/File:Melting_icecubes.gif

Yet Newton’s laws of motion do allow the below event to occur, as well:

Water molecules move randomly in water – so by sheer chance, couldn’t they all come together to spontaneously form ice cubes? Yet this obviously never happens.

melting-ice-reverse-gif

The following is from: Entropy Explained, With Sheep: From Melting Ice Cubes to a Mystery About Time
By Aatish Bhatia, https://aatishb.github.io/entropy/

Imagine you could zoom in and see the atoms and molecules in a melting cube of ice. If you could film the motion of any particle, and then play that film back in reverse, what you’d see would still be perfectly consistent with the laws of physics. It wouldn’t look unusual at all.

The movements of the atoms and molecules in the first gif are every bit as ‘legal’ (in the court of physical law) as those in the second gif.

So why is the first gif an everyday occurrence, while the reverse one impossible?

This isn’t just about ice cubes. Imagine you dropped an egg on the floor. Every atomic motion taking place in this messy event could have happened in reverse. The pieces of the egg could theoretically start on the floor, hurtle towards each other, reforming into an egg as it lifts off the ground, travel up through the air, and arrive gently in your hand. The movement of every atom in this time-reversed egg would still be perfectly consistent with the laws of physics. And yet, this never happens.

So there’s a deep mystery lurking behind our seemingly simple ice-melting puzzle. At the level of microscopic particles, nature doesn’t have a preference for doing things in one direction versus doing them in reverse. The atomic world is a two-way street.

And yet, for some reason, when we get to large collections of atoms, a one-way street emerges for the direction in which events take place, even though this wasn’t present at the microscopic level. An arrow of time emerges.

Entropy of perfume spreading in a room

from http://www.physics.usyd.edu.au/teach_res/mp/doc/tp_equilibrium.htm

We will consider the act of releasing a small quantity of perfume into a fully closed room, from one location within the room. Immediately after the perfume is released, the perfume molecules are in an orderly state (state with the lowest entropy) since all the molecules are located within a small volume element of the room.

After some time interval (t) …. the perfume molecules will be uniformly spread around the room. This is the most disordered state (state of maximum entropy state of maximum probability).

…we’ll never see all the molecules again go back into the small volume they were released from – although the laws of motion, conservation of energy, and conservation of momentum would allow this.

Yet it never happens. Why? Because if all the perfume molecules were suddenly found within the initial volume element it would be a violation of the Second Law of Thermodynamics.

Gas entropy second law thermodynamics

This pic is from http://www.physics.usyd.edu.au/teach_res/mp/doc/tp_equilibrium.htm

Third law of thermodynamics

3. You can’t get out of the game (because getting down to absolute zero is unattainable).

OR

Or the 3rd law is decribed like this:

Siabal Mitra,  professor of physics at Missouri State University, states:

“it would require an infinite number of steps to reach absolute zero, which means you will never get there. If you could get to absolute zero, it would violate the Second Law, because if you had a heat sink at absolute zero, then you could build a machine that was 100 percent efficient.”

Because absolute zero is physically unattainable, the Third Law may be restated as:

the entropy of a perfect crystal approaches zero, as its temperature approaches absolute zero.

What is the Third Law of Thermodynamics? Live Science

Giancoli Chap 15

Questions

In complete sentences or paragraphs, write your answers on a separate sheet of paper

1. Thermodynamics is based on ….

2. How is the zeroth law of thermodynamics like the simplest algebraic property?

3. In one sentence, describe the 1st law of thermodynamics

4. How do our bodies demonstrate the 1st law?

5. In one sentence, describe the 2nd law of thermodynamics

6. Click on the refrigerator link: explain how refrigerators work

7. Consider the image of the man tossing a bunch of bricks: how does this illustrate the concept of entropy?

8. Consider the animations of ice in water. According to Newton’s laws of motion, and laws of momentum, both cases are possible. Yet in the real world we only see one of these events happen. Why doesn’t the other event happen?

9. Consider perfume spreading in a room (you’ll need to watch it for a while to see the whole cycle) According to Newton’s laws of motion, and laws of momentum, all the perfume could eventually come back to where it started. So why doesn’t that happen?

10. According to the third law, what temperature can we never quite reach?

11. Click the link for perpetual motion machines. A perpetual motion machine of the first kind would be tremendous. Great. Beautiful. Amazing 😉 But it’s impossible: Explain why.

12. A perpetual motion machine of the second kind would also be great! And they seem reasonable: they do not violate the 1st law of thermodynamics/law of conservation of energy. But regrettably, this class of perpetual motion machines also doesn’t really work: Why not?

Perpetual motion machines

A perpetual motion machine is a hypothetical machine that can do work indefinitely, without an energy source.  Perpetual-motion-machines

The arrow of time

Why does time never go backward? The answer apparently lies not in the laws of nature, which hardly distinguish between past and future, but in the conditions prevailing in the early universe.

The Arrow of Time, Scientific American article. David Layzer

Is the Universe Leaking Energy? Total energy must be conserved. Every student of physics learns this fundamental law. The trouble is, it does not apply to the universe as a whole. By Tamara M. Davis

Is The Universe Leaking Energy? Scientific American article

 

Related articles

The Quantum Thermodynamics Revolution

 

Quotes

If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.

Sir Arthur Stanley Eddington, The Nature of the Physical World (1915), chapter 4

The second law of thermodynamics is, without a doubt, one of the most perfect laws in physics. Any reproducible violation of it, however small, would bring the discoverer great riches as well as a trip to Stockholm. The world’s energy problems would be solved at one stroke. It is not possible to find any other law (except, perhaps, for super selection rules such as charge conservation) for which a proposed violation would bring more skepticism than this one. Not even Maxwell’s laws of electricity or Newton’s law of gravitation are so sacrosanct, for each has measurable corrections coming from quantum effects or general relativity. The law has caught the attention of poets and philosophers and has been called the greatest scientific achievement of the nineteenth century. Engels disliked it, for it supported opposition to Dialectical Materialism while Pope Pius XII regarded it as proving the existence of a higher being.

  • Ivan P. Bazarov, “Thermodynamics” (1964)

Nothing in life is certain except death, taxes and the second law of thermodynamics. All three are processes in which useful or accessible forms of some quantity, such as energy or money, are transformed into useless, inaccessible forms of the same quantity. That is not to say that these three processes don’t have fringe benefits: taxes pay for roads and schools; the second law of thermodynamics drives cars, computers and metabolism; and death, at the very least, opens up tenured faculty positions.

Seth Lloyd, writing in Nature 430, 971 (26 August 2004)

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?

– C. P. Snow, 1959 Rede Lecture, “The Two Cultures and the Scientific Revolution”.

The Two Cultures Snow.PNG

External resources

What is a simple definition of the laws of thermodynamics? PhysLink

http://www.nmsea.org/Curriculum/Primer/what_is_entropy.htm

http://entropysimple.oxy.edu/content.htm

http://study.com/academy/lesson/what-is-entropy-definition-law-formula.html

http://www.chem1.com/acad/webtext/thermeq/TE1.html

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-PS3-2. Develop and use a model to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles and objects or energy stored in fields.
Clarification Statements: Examples of phenomena at the macroscopic scale could include evaporation and condensation, the conversion of kinetic energy to thermal energy,

HS-PS3-4a. Provide evidence that when two objects of different temperature are in thermal contact within a closed system, the transfer of thermal energy from higher temperature objects to lower-temperature objects results in thermal equilibrium, or a more uniform energy distribution among the objects and that temperature changes
necessary to achieve thermal equilibrium depend on the specific heat values of the two substances. Energy changes should be described both quantitatively in a single phase (Q =m·c·∆T) and conceptually either in a single phase or during a phase change.

Next Generation Science Standards

Influence of Science, Engineering and Technology on Society and the Natural World: Modern civilization depends on major technological systems. Engineers continuously modify these technological systems by applying scientific knowledge and engineering design practices to increase benefits while decreasing costs and risks. (HS-PS3-3)

Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. (HS-PS3-3)

Energy cannot be created or destroyed—only moves between one place and another place, between objects and/or fields, or between systems. (HS-PS3-2)

AP Physics

7.B.2.1: The student is able to connect qualitatively the second law of thermodynamics in terms of the state function called entropy and how it (entropy) behaves in reversible and irreversible processes. [SP 7.1]
– AP Physics Course and Exam Description

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