SCEINCE

What are the first two laws of thermodynamics and why do they matter


Thermodynamics is a branch of physics that studies the relationship between heat and other forms of energy. It is particularly focused on the transmission and conversion of energy and has made many contributions to the fields of chemical and mechanical engineering, physical chemistry and biochemistry.

The term “thermodynamics” was probably first introduced by the mathematician physicist William Thompson, also known as Lord Kelvin, in his article On the dynamic theory of heat (1854).

Modern thermodynamics is based on four laws:

  • IN zero law of thermodynamics states that if two independent thermodynamic systems are in thermal equilibrium with a third system (meaning that there is no net flow of heat energy between them), they are also in thermal equilibrium with each other.
  • IN first law of thermodynamics, also known as the Energy Conservation Act, reads that energy cannot be created or destroyed, but only transformed or transferred.
  • IN second law of thermodynamics confirms that the the entropy of an isolated system always increases with time.
  • IN the third law of thermodynamics finds that the entropy of the system approaches a constant value when the temperature approaches absolute zero.

In this article we will focus on first and second laws of thermodynamics.

What are they first and second laws of thermodynamics?

The first law of thermodynamics is also known as energy conservation law. Given that energy cannot be created or destroyed, the total energy of one isolated system it will always be constant, because it can only be converted into another form of energy or transferred elsewhere in the system.

The formula of the first law of thermodynamics is ΔU = Q – W, where ΔU is the change in the internal energy U of the system, Q is the net heat transferred to the system (the sum of all heat transfers of the system), and W is the net work done by the system (the sum of all work done on or by the system).

The second law introduces the concept of entropy in thermodynamics. Entropy is a physical property that measures the amount of heat energy in a system that is not available to perform useful work. The energy that cannot work is converted into heat, and the heat increases the molecular disorder of the system. Entropy can also be seen as a measure of this disorder.

Source: OpenStax / Wikimedia Commons

The second law of thermodynamics states that entropy always increases. This is because in any isolated system there is always a certain amount of energy that is not available to do the job. Therefore, heat will always be produced and this naturally increases the disorder (or entropy) of the system.

The increasing entropy (ΔS) is equal to the heat transfer (ΔQ) divided by the temperature (T). Therefore, the second law of thermodynamics can be expressed by the formula ΔS = ΔQ / T.

Who discovers the laws of thermodynamics?

As noted above, the first law of thermodynamics is closely related to the law of conservation of energy, which was first expressed by Julius Robert Meyer in 1842. Meyer realized that the chemical reaction produces heat and work and that work can after this to produce a certain amount of heat. Although this is essentially a statement about conserving energy, Mayer was not part of the scientific institution and his work was ignored for several years.

Instead, the German physicist Rudolf Clausius, the Irish mathematician William Thomson (Lord Kelvin) and the Scottish mechanical engineer William Rankin would play a greater role in the development of the science of thermodynamics and the adaptation of energy conservation to thermodynamic processes beginning around 1850.

Rudolf Clausius, Lord Kelvin and William Rankin
Rudolf Clausius, Lord Kelvin and William Rankin. Source: Wikimedia Commons.

The second law of thermodynamics originates from the work of the French mechanical engineer Nicolas Leonard Sadi Carnot, who studied steam engines. He is often considered the father of thermodynamics thanks to his book Reflections on the driving force of fire (1824), which presents a theoretical discussion of the perfect (but unattainable) heat engine “Engine power” is what we would call work today, and “fire” refers to heat.

In this book, Sadi Carnot wrote an early exposition of the second law of thermodynamics, which was reformulated by Rudolf Clausius more than forty years later. Other scholars have also contributed to the definition of the law: the aforementioned Lord Kelvin (1851), the German mathematician Max Planck (1897) and the Greek mathematician Constantine Carateodori (1909).

According to researcher in thermal sciences Jayaraman Srinivasan, the discovery of the first and second laws of thermodynamics was revolutionary in 19th century physics.

The third law of thermodynamics was developed by the German chemist Walter Nernst in the early 20th century. Nernst demonstrates that the maximum work obtained from a given process can be calculated from the heat given off at temperatures close to absolute zero. The zero law has been studied since the 1870s, but was defined as a separate law in the 1900s.

How are the first and second laws of thermodynamics related?

The first and second laws of thermodynamics are independent of each other, since the law of entropy is such are not directly extracted or derived from the law of conservation of energy or vice versa.

But at the same time the two laws complement each other, because while the first law of thermodynamics involves the transfer or transformation of energy, the second law of thermodynamics speaks of the direction of physical change – how isolated or closed systems move from lower to higher entropy due to energy that cannot be used for operation.

In other words, the second law of thermodynamics takes into account the fact that the energy transformation described in the first law of thermodynamics always releases some additional, “useless” energy that cannot be turned into work.

Why are the first and second laws of thermodynamics important?

The laws of physics explain how natural phenomena and machines work. These explanations not only satisfy our curiosity, but also allow us to predict phenomena. In fact, they play an important role in allowing us to build functional machines.

As a branch of physics, thermodynamics is no exception. If you know how much energy in a system can be used for work and how much will be converted into heat (and there is always a certain amount of “useless” energy in the system), you can predict how much heat a machine will produce under different conditions. Then you can decide what to do with this heat.

Heat is a form of energy, and if you know that energy cannot be destroyed, but only transformed, you could find a way to turn that heat into mechanical energy – which is what heat engines actually do.

Heat engine
Scheme of the heat engine. Source: Gonfer / Wikimedia Commons

Given this basically application of the first and second laws of thermodynamics, you can probably imagine how useful they can be in the field of engineering. But they can also have applications in chemistry, cosmology (entropy predicts the eventual thermal death of the universe), atmospheric sciences, biology (plants convert radiant energy into chemical energy during photosynthesis) and many other fields. Hence the importance of thermodynamics

Can you violate the first two laws of thermodynamics?

To violate the first law of thermodynamics, we will have to create a machine with “perpetual motion” that works continuously without introducing any power. This does not yet exist. All machines we know receive energy from a source (thermal, mechanical, electrical, chemical, etc.) and convert it into another form of energy. For example, steam engines convert heat energy into mechanical energy.

In order to violate the first law of thermodynamics, life itself must be rethought. Living beings also exist in accordance with the law of conservation of energy. Plants use photosynthesis to make “food” (chemical energy for their use), and animals and humans eat to survive.

Nutrition is basically the extraction of energy from food and its conversion into chemical energy (stored as glucose), which actually gives us “energy”. We convert this chemical energy into mechanical energy when we move, and into thermal energy when we regulate our body temperature, and so on.

But things may be a little different in the quantum world. In 2002, chemical physicists at the Australian National University in Canberra demonstrated that the second law of thermodynamics could be violated briefly on an atomic scale. The scientists placed latex beads in water and captured them with a precision laser beam. Regularly measuring the motion of the grains and the entropy of the system, they noticed this the change in entropy is negative at time intervals of a few tenths of a second.

Recently, researchers, including some working on the Google Sycamore quantum processor, have created “time crystals”, outside the equilibrium phase of unlimited rotation of matter between two energy states, without loss of energy for the environment. These nanoparticles never reach thermal equilibrium. They form a quantum system that does not seem to increase its entropy – which completely violates the second law of thermodynamics.

This is a real-life demonstration of Maxwell’s demon, a thought experiment to violate the second law of thermodynamics.

Proposed by the Scottish mathematician James Clerk Maxwell in 1867, the experiment consisted of placing a demon in the middle of two gas chambers. The demon controlled a massless door that allowed the chambers to exchange gas molecules. But given that the demon opened and closed the door so fast, only fast-moving molecules passed in one direction and only slow-moving molecules in the other. In this way, one chamber is heated and the other is cooled, reducing the total entropy of the two gases without including operation.

Maxwell's demon
Source: Htkym / Wikimedia Commons

Although we still do not know exactly how to use the crystals of time, this is already considered a revolutionary discovery in the physics of condensed matter. Time crystals could at least significantly improve the technology of quantum computing.

But there is also something in the concept of “perpetual motion without any energy” that inevitably leads futuristic minds to imagine quantum devices with perpetual motion that will not require any additional energy input – such as a switched off refrigerator that is still can cool food down; or more sci-fi, a a supercomputer that supports the simulation we could live in.





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