In the world of physics, there is a branch that studies the transformations that occur due to heat and work in a system. This is thermodynamics. It is a branch of physics that studies all the transformations that result solely from processes involving changes in the state variables of both temperature and energy at a macroscopic level. To delve deeper into this topic, you can consult the principles of thermodynamics and also the systems of temperature units.
In this article we are going to tell you everything you need to know about thermodynamics and the principles of thermodynamics.
Key features
If we do an analysis of classical thermodynamics we see that it is based on the concept of macroscopic system. This system is nothing more than a portion of physical or conceptual mass that is separated from the external environment. In order to better study thermodynamic systems, it is always assumed that it is a physical mass that is not disturbed by the exchange of energy with the external ecosystem.
The state of a macroscopic system in equilibrium is specified by quantities called thermodynamic variables. These variables are all familiar: temperature, pressure, volume, and chemical composition. They define systems and their equilibrium. The main notations used in chemical thermodynamics have been established by the International Union of Applied Thermodynamics (IUPAC). These units allow for a better understanding and explanation of the laws of thermodynamics. Furthermore, the study of entropy is also fundamental in this field.
However, there is a branch of thermodynamics that does not study equilibrium, but rather analyzes thermodynamic processes characterized primarily by their inability to achieve stable equilibrium conditions. This relates to the importance of understanding the behavior of thermodynamic cycles in these processes.
laws
These principles were formulated during the 19th century and govern all transformations and their progression. They also define the real limits for achieving a true understanding. They are axioms that cannot be proven but are indemonstrable based on experience. All theories of thermodynamics are based on these principles. We can distinguish three basic principles plus the zeroth law, which defines temperature and is implicit in the other three.
Zero law
Let's describe this zeroth law, which is the first law that describes temperature, which is implicit in the rest of the principles. When two systems interact with each other and are in thermal equilibrium, they share some properties. These shared properties can be measured and given a numerical value. As a result, if the two systems are in equilibrium with a third system, they will be in equilibrium with each other, and the shared property is temperature.
Therefore, this zeroth law simply states that if body A is in equilibrium with body B, and body B is in thermal equilibrium with body C, then bodies A and C will also be in thermal equilibrium. This principle helps us understand heat exchange between bodies at different temperatures. For those who wish to better understand these laws, I recommend visiting the page on branches of physics.
First Law of Thermodynamics
When a body is placed in contact with a colder body, a transformation occurs that leads to a state of equilibrium. This state of equilibrium is based on the temperature of the two bodies being equal, since an energy transfer takes place between the hot body and the cold body. To explain this phenomenon, scientists assumed that a hot substance, present in greater quantities, would pass to the colder body. They considered a fluid that could move through the mass to exchange heat.
This principle identifies heat as a form of energy. It is not a material substance. In this way, it was demonstrated that heat, measured in calories, and work, measured in joules, are equivalent. Therefore, we know today that 1 calorie is approximately 4,186 joules.
The first principle of thermodynamics can be said to be a principle of conservation of energy. A quantity of energy in a heat engine is converted into work, and no engine can produce that work without consuming energy. We can state this first principle as follows: the change in the internal energy of a closed thermodynamic system is equal to the difference between the heat supplied to the system and the work done by the system on the environment.
Second law of thermodynamics
This principle states that it is impossible to create a cyclic machine whose sole result is the transfer of heat from a cold body to a hot body. In other words, it is impossible to carry out a transformation whose only outcome is to convert heat extracted from a single source into mechanical work.
This principle denies the possibility of perpetual motion of the second kind. We know that the entropy of a system remains isolated and unchanged when a reversible transformation occurs. We also know that it increases when an irreversible transformation occurs.
Third law of thermodynamics
This last principle is closely related to the second and is considered a consequence of it. This principle states that absolute zero cannot be reached in a finite number of transformations. We know that absolute zero is simply the lowest possible temperature. In Kelvin, it is 0, but in degrees Celsius, it has a value of -273.15 degrees.
It also establishes that the entropy for a perfectly crystalline solid at a temperature of 0 Kelvin is equal to 0. This means that there would be no entropy, so the system would be completely stable. The release, translational, and rotational energies of the particles comprising it would be zero at a temperature of 0 Kelvin.
I hope that with this information you can learn more about thermodynamics and basic principles.