The Laws of Thermodynamics
By: James Christian N. Domingo


Thermodynamics has got numerous definitions – differences depend on who you ask. In science, thermodynamics is defined as “the study of conversion of heat into work through the intermediate actions of a system.” A thermodynamicist would say it is “is the science of everything – meaning the behavior of any body in the universe.” A physicist would say it is “the study of the principles and laws behind the phenomenon of the production of motion by heat, considered from a sufficiently general point of view.” From everything that I have read so far and from what I have studied in my Chemistry classes so far, I would say that thermodynamics is the study of the relationship between a system’s behavior with temperature.

Zeroth Law of Thermodynamics
The zeroth law of thermodynamics is not well discussed because a lot of people do not consider it as a law of thermodynamics. It is considered to be a common knowledge, but nonetheless, it is still on of the basic principles of thermodynamics.
The zeroth states that at equilibrium the temperature of any body is constant throughout its parts. This means that when a warmer object meets a cooler object, the energy would flow into the cooler object to raise its temperature. The energy transfer would stop when the temperature of both parts are constantly equal.

First Law of Thermodynamics
The first law of thermodynamics state that the energy in a closed system can neither be created nor destroyed. This idea also leads to a conclusion that the energy of the whole universe is constant. However, what is important to know is that if an external energy is applied to a system, then the internal energy of the system increases. Thus leading to the equation:

ΔE = q + w

The change in amount of energy contained by the system is represented in the equation as ΔE, whereas the heat added to the system is represented by the q and the work done by the system is represented by w.

Second Law of Thermodynamics
The second law of thermodynamics introduces the properties of entropy, which is shown in equations as S. Entropy is a measure of disorder or the amount of energy lost because it has turned into energy unavailable for work. The second law of thermodynamics state that a process that starts in equilibrium and finishes in another, will always tend to move to the direction in which the entropy is increased. In other words, things would most likely go in a disordered way, rather than the ordered way. Similarly, 20 kids tend to walk around a classroom rather than sit accordingly in their seats. From here we can conclude that heat cannot be converted without losing some of its amount. Every time energy is converted, energy is always lost in numerous ways. The equation that calculates the change in entropy of a reaction is as follows:

ΔS = Δq/T

ΔS is the change in entropy after a reaction has taken place, Δq is the change in heat and T is the amount of time the reaction took. Also, the entropy of a system is constantly increasing, even if it is resting. Similarly, no matter how hard you try to ensure an outcome, there will always be a case where it would fail. An example would be a arranging a dozen pennies in a stack and tipping it to one side so all would fall down with the same faces up. Although the probability is high, it is never 100% sure.
Since pressure is a factor that affects the energy of a system, an equation was created to relate the changes in entropy and enthalpy of reactions. Thus, the Gibb’s Free Energy theorem was created. Gibb’s free energy, or G, is defined as follows:

ΔG = ΔH – (TΔS)

ΔH is the change in energy after the reaction; T is the time it took for the reaction to occur and ΔS is the change in entropy after the reaction.

The following video talks about the 2nd law of thermodynamics.

Third Law of Thermodynamics
The third law of thermodynamics state that it is impossible to cool an object down to an absolute zero because it would require an infinite amount of energy. An object with an absolute zero temperature would mean that all its particles have stopped moving, thus creating a perfect crystal. According to the second law, it is impossible to make a substance reach absolute zero because entropy is always increasing and particles would always tend to disordered.

The chart below summarizes the basic points of the zeroth, first, second, and third laws of thermodynamics:

Fourth Law of Thermodynamics and more…
The fourth and the last law of thermodynamics might be interesting to some. This law states that it is not possible to identify another law of thermodynamics, besides the first three that were mentioned (this would also include the zeroth law – which is not really considered as a law of thermodynamics). However, there were still few more laws that were proposed to be additional laws of thermodynamics.

History and Development

Much similar to any scientific laws and principles, the laws of thermodynamics was formed by numerous experimentation and innovations. Scientists from different time periods have helped shape the laws of thermodynamics that we accept today.
The basic principles of heat and temperature were first established in 1600’s, where scientists during that time believed that heat is related with the motion of the small particles that make up an object. However in 1700, scientists changed their idea about heat. The believed that heat was a substance similar to a liquid that is completely separate from the object itself.

In the mid 1800’s scientists who disbelieved this conclusion performed experiments that helped put the previous notion about heat in doubt. James Prescott Joule is one of the scientists who performed such experiments. James Joule did extensive research that proved different forms of energy, including electrical, mechanical and heat, can be changed from one from to another. These studies gave way for the further development of the laws of thermodynamics. Sadi Carnot was another important contributor to the development of thermodynamics. He hoped to improve the performance of mills and factories in France so he studied the principles that involve dealing with machines. The studies of both these men helped start thermodynamics.

In the late 18th century, Joseph Black performed a few experiments that allowed him to reach a conclusion that became the zeroth law of thermodynamics. With the help of thermometers, he was able to measure temperatures of certain areas of a particular body. He noted that heat flowed from warmer object and into a cooler object, and that this flow will stop once equilibrium has been reached. He called this state as thermal equilibrium.

In 1850, Rudolf Clausius solidified thermodynamics into writing. He combined and refined the works of James Joule and Sadi Carnot in his textbooks. Clausius refined Carnot’s work by adding the concept of entropy in his studies. Joule’s idea of the conservation of energy and Carnot’s studies on energy with machines, he stated the outline of first and second main principles of thermodynamics (presently known as the first and second law of thermodynamics).

Clausius was not the only one working on these theorems; Ludwig Boltszman is also suggesting a few equations that can help explain the second law of thermodynamics in a mathematical way. At first Clausius suggested that entropy is a ratio of heat to temperature. Boltzman, on the other hand, suggested a couple of equations more. None of them completely defined the second law of thermodynamics. In 1870’s, Maxwell and Kelvin pointed out that all the failures of the previous scientists were due to the fact that they were not able to track the movement of large numbers of molecules. Therefore, they suggested that entropy is related to the unpredictability of molecular movement. Around the 1990’s, Willard Gibbs presented how a systems can go from different states at different times. He was able to derive an equation that free energy and spontaneity of chemical reactions.

James Dewar, a Scottish physicist, has done research on low temperature matters. He had completely solidified hydrogen and reached 13 degrees above absolute zero. From his studies, he concluded that the closer you get to absolute zero, the more work you would have to put in. From Dewar’s observations, the third law of thermodynamics was proposed by Walther Nernst, a German physicist. Nernst proposed a heat theorem that involves free energies and equilibrium at different temperatures. After a few years, another German physicist, Max Planck, suggested that Nernst’s theorem could be a new entropy theorem.

The fourth law was stated in 1952, by Lars Onsager. He said that there cannot be a fourth law besides the three that were already existing (the zeroth law including). However, this law did not stop other scientist and researchers to come up with additional laws in thermodynamics. There were ideas proposed to be the fifth and sixth laws of thermodynamics.

Common Uses and Applications

The first law of thermodynamics can be applied in cyclic process, where systems return into their initial state. The internal energy of the system is not changed and they are restored to their initial state. An engine for example, would return to its initial state after it has performed work, in this case combustion of fuel and the movement of an automobile. Cooling machines, like refrigerators and air conditioners, also use the principles of the first law of thermodynamics. Air conditioners use the change in pressure of air to decrease its temperature, thus absorbing the heat of its surroundings.

Any transfer of heat from an object to another uses the laws of thermodynamics. Processes that include conduction, convection and radiation are ways in which heat can be transferred. A lot daily activities involve these processes.

The second law of thermodynamics is used when creating engines or any form of converting energy from one form to another. Sadi Carnot, one of the founders of the idea that had evolved into the second law, was motivated by his desire to create efficient steam engines during his time. The second law helped in the creation of combustion engines. Today, engineers use the second law of thermodynamics to create efficient engines. Engineers involved in fossil fuel energy conversion may use the second law to convert fossil fuels as efficiently as possible.


Brightstorm. (Producer). (n.d.). Second law of thermodynamics. Retrieved on May 5, 2011 from
Fourth law of thermodynamics. (n.d.). Retrieved from
James joule prescott. (n.d.). Retrieved from
Khemani, Haresh. (2008, August 13). Application of second law of thermodynamics: part-1: automobile engines. Retrieved from
Thermodynamics. (n.d.). Retrieved from
Thermodynamics - real-life applications. (n.d.). Retrieved from
Third law of thermodynamics. (n.d.). Retrieved from
Wolfram, Stephen. (2002). A new kind of science. Retrieved from
Zeroth law of thermodynamics . (n.d.). Retrieved from
WonderslugV. (Producer). (2007). Laws of Thermodynamics. Retrieved on May 13, 2011 from:

Further Reading
Here are some links that shows the works of the important scientists that helped shape the laws of thermodynamics. Hopefully, reading about their works would help you understand about the laws of thermodynamics as how they have helped me.

Sadi carnot. (n.d.). Retrieved from

Rudolf clausius. (n.d.). Retrieved from

James maxwell. (n.d.). Retrieved from

Willard gibbs. (n.d.). Retrieved from