# thermodynamics

2022

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

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, strength") to the branch of physical 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, the internal energy or the volume; as well as non-extensive variables such as temperature, the Pressure or the chemical potential, among other types of magnitudes.

However, thermodynamics does not offer an interpretation of the quantities 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 acting on them. For that reason, consider that the Energy can only be exchanged from one system to another as a heat or from job.

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. Following this invention, scientists Robert Boyle and Robert Hooke they refined their systems and looked at the correlation between pressure, temperature, and volume. Thus were born the principles of thermodynamics.

## Thermodynamic system

Open systems exchange energy and matter with their environment.

A thermodynamic system is understood as a part of the universe that, for study purposes, is conceptually isolated from the rest and tries to understand autonomously. Take note of the ways in which energy changes or is preserved and, at the same time, of 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 criterion for classifying 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 of the known systems do in everyday life. For example: a car. One hands him fuel and it returns to the environment gases And heat.
• 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 content is invariable, but loses heat with theweather, dissipating it into the air around it.
• 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 some degree: a thermos that contains Water hot will preserve its temperature for a while, enough to keep it insulated for a while.

## Laws of thermodynamics

The "zero law" is logically expressed like this: 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. Said principles or laws are:

• First principle, or Law of Conservation of energy. It states 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 ones. In fewer words: "Energy cannot be created or destroyed, only transformed."
• Third Principle, or Law of Absolute Zero. It dictates that the entropy of a system that is brought to absolute zero will always be a definite constant. This means that when 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 "zero law" because, although it was the last to run, the basic and fundamental precepts it establishes take precedence 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 the chemical reactions, all framed in 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, in order 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 every time a spontaneous reaction occurs.

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