Three Laws of Thermodynamics

Written By technology factory on Sunday, 4 December 2011 | 17:37

Thermodynamics is the study of energy, the conversion of energy between various forms and the ability of energy to do work. Initially, three laws of thermodynamics were posited. There seems to be a fourth, called the Zeroth Law, because Laws 1, 2, and 3 were spoken for. 

C.P. Snow, the British scientist and author has offered up an easy and funny way to remember the Three Laws. He says they can be translated as: (1) you cannot win
(you can’t get something for nothing because matter and energy are conserved. (2) You cannot break even (you cannot return to the same energy state because entropy always increases (3) you cannot get out of the game (because absolute zero is not attainable). 

So, what do these laws really say and why are they important? In simple terms, the Laws dictate the requirements for heat and work. They were generated during the 19th century as the industrial revolution took hold and grew. Physicists became involved with studying the flow of heat from machines as well as the chemical changes that accompanied the actual work. They were interested in gaining maximum efficiency. In other words, they wanted to create a perpetual motion machine, or one that could run off its own heat it created during the process of work, so it could do more work, create more heat and …you get the point. 

Unfortunately for the machines owners, the physicists failed. Basically they showed that a perpetual motion machines was impossible. In so doing, they came up with the Three Laws of Thermodynamics. 

The First Law basically says that energy or matter can neither be created nor destroyed. In terms of the machine, this meant that the total energy output (work by the machine) is equal to the heat supplied. In other words, the change in the internal energy of a closed system is equal to the heat added to the system minus the work done by the system. Because the system operates in the real world, some energy always escapes into the outside world, thus leading to both inefficiency and the Second Law, which was generated to cover the so-called flaw in the First Law. 

The Second Law essentially says that it is impossible to obtain a process where the unique effect is the subtraction of a positive heat from a reservoir and the production of a positive work. Energy exhibits entropy. It moves away form its source. In this sense, energy or heat cannot flow form a colder body to a hotter body. You cannot keep a continual flow of heat to work to heat to work without adding energy to the system. In machine terms, you have to add energy to get more work, and the ratio of heat to work will never equal 100% due to energy expanding away from its source. 

The Third Law explains this further. It says that all processes cease as temperature approaches absolute zero. This is the temperature at which molecules cease movement, cease producing kinetic energy. In other words, there is no energy. 

With the First Law, we know that matter/energy can neither be created nor destroyed. It can change form, as in solid to liquid to gas to plasma and back again, but the amount of matter/energy in the system (the universe) stays constant. The Second Law says that while the quantity of matter/energy remains the same, the quality deteriorates over time. How could this happen? 

Usable energy is used for productivity, growth, and repair. In the course of this process, usable energy is converted into unusable energy, and usable energy is thus lost in the form of unusable energy. Entropy is used as a measure of unusable energy in a closed system. As it increases and usable energy decreases by the same amount (First Law) randomness increases. As said earlier, energy retreats from its source and generally in the form of unusable energy. 

As an incredibly simple illustration, think of a fire. As you add wood (matter), what is produced is heat (which then moves into the surrounding environment), and smoke and water vapor, which again escapes into the surrounding environment, and eventually ash, which gives up its last remaining heat to the surrounding environment. You are left with cold,dlead ash which has taken on a random form which is not seemingly related to the original form of the wood. 

The so-called Zeroth Law is a bit more fundamental than the other Three Laws. It came into being after the Three. It essentially says that if each of two systems is in equilibrium with a third system, the first two are in equilibrium with one another. 

An easy way to illustrate this in physical terms. John weighs the same as Bill. Sam weighs the same as Bill. Therefore John and Sam weigh the same. While the Zeroth Law describes much more complicated systems, the essentials are the same. 

Of these Laws of Thermodynamics the Second Law is the most powerful, and has the most implications. It is even present in the popular culture. No less a personage than Homer Simpson once said, “In this house, we obey the Second Law of Thermodynamics”. 

Seriously, the Second Law basically says that the universe is constantly losing usable energy and never gaining. We also know that the universe is constantly expanding, as predicated by the Second Law, the Law of Entropy. We can conclude that the universe is finite. We could also conclude that the universe had a specific beginning, the moment of “Zero Entropy” What does this mean? 

One person described this condition in terms of a wind-up clock. Once wound tightly, it begins to slowly wind down until it reaches the end. The question is not when it will run down or when the universe will end. The question is…Who wound the clock? Robert Jastrow, a NASA scientist said that if the universe was some sort of cosmic egg in the beginning and then hatched, it logically required a cosmic chicken.

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