Thermodynamics (Meaning and Explanation)

We explain what thermodynamics is and what a thermodynamic system consists of. Also, what are the laws of thermodynamics.

Thermodynamics - thermal equilibrium — Energy can only be exchanged from one system to another as heat or work.

What is Thermodynamics?

It is called thermodynamics (from the Greek thermos“heat” and dynamos“power, force”) to the branch of physics that studies the mechanical actions of heat and other similar forms of energy. His study approaches objects as real macroscopic systems, through the scientific method and deductive reasoning, paying attention to extensive variables such as entropy, internal energy or volume; as well as non-extensive variables such as temperature, pressure or chemical potential, among other types of magnitudes.

However, the thermodynamics does not offer an interpretation of the magnitudes it studies and its objects of study are always systems in a state of equilibrium, that is, those whose characteristics are determinable by internal elements and not so much by external forces that act on them. For this reason, it is considered that energy can only be exchanged from one system to another as heat or work.

The formal study of thermodynamics began thanks to Otto von Guericke in 1650 a German physicist and jurist who designed and built the first vacuum pump, refuting Aristotle and his maxim that “nature abhors a vacuum” with his applications. After this invention, scientists Robert Boyle and Robert Hooke perfected their systems and observed the correlation between pressure, temperature and volume. Thus the principles of thermodynamics were born.

thermodynamic system

A thermodynamic system is understood to be a part of the universe that, for study purposes, it is conceptually isolated from the rest and an attempt is made to understand it autonomously Take note of the ways in which energy changes or is preserved and, at the same time, its exchanges of matter and/or energy with the environment or with other similar systems (if any). It is, therefore, a method of studying thermodynamics.

The main classification criterion of these systems is based on their degree of isolation from the environment, thus distinguishing between:

Open systems. Those that freely exchange energy and matter with their environment, as most known systems do in everyday life. For example: a car. You give it fuel and it returns gases and heat to the environment.
Closed systems. Those that exchange energy with their environment, but not matter. This is what happens with a closed container, such as a can, whose contents are unchanged, but lose heat over time, dissipating it into the surrounding air.
Isolated systems Those that, to a certain extent, do not exchange energy or matter with the environment. There are no perfectly insulated systems, of course, but there are to a certain degree: a thermos containing hot water will maintain its temperature for a while, enough to remain insulated for a while.

Laws of thermodynamics

Thermal balance — The “zero law” is logically expressed as follows: if A = C and B = C, then A = B.

Thermodynamics is governed by what is established in its four fundamental principles or laws, formulated by various scientists throughout the history of this discipline. These principles or laws are:

First principle, or Law of Conservation of energy. It establishes that the total amount of energy in any physical system isolated from its environment will always be the same, although it can be transformed from one form of energy to many different others. In fewer words: “Energy can neither be created nor destroyed, only transformed.”
Third principle, or Law of absolute zero. It dictates that the entropy of a system that is taken to absolute zero will always be a definite constant. This means that upon reaching absolute zero (-273.15° C or 0 K), the processes of physical systems stop and the entropy has a constant minimum value.
Zero principle or Law of thermal equilibrium. It is called “law zero” because, although it was the last to be postulated, the basic and fundamental precepts it establishes have priority over the other three laws. It dictates that “if two systems are in thermal equilibrium independently with a third system, they must also be in thermal equilibrium with each other.”

Chemical thermodynamics

Chemical thermodynamics is a separate field of study, focused on the correlation between heat and work, and chemical reactions all framed within what is established by the principles of thermodynamics. That is, it is about the application of the laws of thermodynamics, especially the first two, to the world of reactions between substances and compounds, to obtain the so-called “fundamental Gibbs equations”, which govern the way in which the chemical energy contained in the different compounds changes and is transmitted, or how the degree of entropy of the universe increases each time a spontaneous reaction occurs.