It is the term used to encompass the series of studies and experiments that are carried out under the laws of physics, which analyze in detail the balance of the terrestrial elements, as well as how heat and energy affect life on the planet and the materials that make it up. From this, it has been possible to create different machines that help in industrial processes. The word comes from the Greek words θερμο and δύναμις, which mean “thermo” and “heat.
What is thermodynamics
Table of Contents
The definition of thermodynamics indicates that it is the science that deals specifically with the laws that govern the transformation of thermal energy into mechanical energy and vice versa. It is based on three fundamental principles and has obvious philosophical implications and also allows the formulation of concepts that are among the most far-reaching in physics.
Within this, different methods of investigation and appreciation of the required objects are used, such as extensive and non-extensive magnitudes.The extensive one studies internal energy, molar composition or volume and the second, for its part, studies pressure, temperature and chemical potential; even so, other magnitudes are used for accurate analysis.
What does thermodynamics study
Thermodynamics studies the exchanges of thermal energy between systems and the mechanical and chemical phenomena that such exchanges imply. In a particular way, it is in charge of studying the phenomena in which there is transformation of mechanical energy into thermal energy or vice versa, phenomena that are called thermodynamic transformations.
It is considered a phenomenological science, since it focuses on the macroscopic studies of objects and others. Similarly, it makes use of other sciences to be able to explain the phenomena it seeks to identify in its objects of analysis, such as statistical mechanics. Thermodynamic systems use some equations that help to mix their properties.
Among its basic principles can be found that of energy, which can be transferred from one body to another, through heat. It is applied to many areas of study such as engineering, as well as collaborating with the development of engines, studying phase changes, chemical reactions and black holes.
What is a thermodynamic system
A thermodynamic system is called the body, or set of bodies, over which a thermodynamic transformation takes place. The study of a system is done starting from the state, that is, from its physical conditions at a given moment. At the microscopic level, said state can be described by means of coordinates or thermal variables, such as mass, pressure, temperature, etc., which are perfectly measurable, but at the microscopic level, the fractions (molecules, atoms) that constitute the system and identify the set of positions and velocities of these particles on which the microscopic properties ultimately depend.
In addition, a thermodynamic system is a region of space that is subject to the study that is being carried out and that is limited by a surface that can be real or imaginary. The region outside the system that interacts with it is called the system environment. The thermodynamic system interacts with its environment through the exchange of matter and energy.
The surface that separates the system from the rest of its context is called a wall, and according to its characteristics they are classified into three types that are:
Open thermodynamic system
It is the exchange between energy and matter.
Closed thermodynamic system
It does not exchange matter, but it does exchange energy.
Isolated thermodynamic system
It does not exchange matter or energy.
Principles of thermodynamics
Thermodynamics has certain fundamentals that determine the basic physical quantities that represent thermodynamic systems. These principles explain what their behavior is like under certain conditions and prevent the emergence of certain phenomena.
It is said that a body is in thermal equilibrium when the heat it perceives and emits are equal. In this case the temperature of all its points is and remains constant. A paradoxical case of thermal equilibrium is an iron exposed to the sun.
The temperature of this body, once equilibrium is reached, remains higher than that of the environment because the continuous contribution of solar energy is compensated by that which the body radiates and loses it with its conduction and convection.
The zero principle of thermodynamics or the zero law of thermodynamics is present when two bodies in contact are at the same temperature after reaching thermal equilibrium. It is easily understood that the coldest body warms up and the warmer one cools, and thus the net flow of heat between them decreases as their difference in temperature decreases.
"> Loading…First Law of thermodynamics
The first principle of thermodynamics is the principle of the conservation of energy (properly and in accordance with the theory of relativity of matter-energy) according to which it is neither created nor destroyed, although it can be transformed in a certain way to another.
The generalization of the energy principle allows us to affirm that the variation of the internal force of a system is the sum of the work carried out and transferred, a logical statement since it has been established that work and heat are the ways of transferring energy and that it is not create or destroy.
Internal energy of a system is understood as the sum of the different energies and of all the particles that compose it, such as: kinetic energy of translation, rotation and vibration, energy of binding, cohesion, etc.
The first principle has sometimes been stated as the impossibility of the existence of the perpetual motive of the first kind, that is, the possibility of producing work without consuming energy in any of the ways in which it manifests itself.
Second principle of thermodynamics
This second principle deals with the irreversibility of physical events, especially at the time of a heat transfer.
A large number of experimental facts demonstrate that the transformations that occur naturally have a certain meaning, without ever being observed, that it is spontaneously carried out in the opposite direction.
The second principle of thermodynamics is a generalization of what experience teaches about the sense in which spontaneous transformations occur. It supports various formulations that are actually equivalent. Lord Kelvin, British physicist and mathematician, stated it in these terms in 1851 "It is impossible to carry out the transformation whose only result is the conversion into work of the heat extracted from a single source of uniform temperature"
This is one of the most important laws of thermodynamics in physics; Even though they can be formulated in many ways, they all lead to the explanation of the concept of irreversibility and that of entropy. The German physicist and mathematician Rudolf Clausius established an inequality that is related between the temperatures of an arbitrary number of thermal sources and the absorbed amounts of heat delivered by them, when a substance goes through any cyclical process, reversible or irreversible, exchanging heat with the sources.
In a Hydroelectric Power Plant, electrical energy is produced from the potential energy of the dammed water. This power is transformed into kinetic energy when the water descends through the pipes and a small part of this kinetic energy is transformed into the rotational kinetic force of a turbine, whose axis is integral with the axis of the inductor of an alternator which generates the force electric.
The first principle of thermodynamics allows us to ensure that in the changes from one form of energy to another there has been neither increase nor decrease of the initial power, the second principle tells us that part of that energy will have been fired in the form of heat.
Third Principle of Thermodynamics
The third law was developed by chemist Walther Nernst during the years 1906-1912, which is why it is often referred to as Nernst's theorem or Nernst's postulate. This third principle of thermodynamics says that the entropy of an absolute zero system is a definite constant. This is because there is a zero temperature system in its ground state, so its entropy is determined by the degeneration of the ground state. In 1912, Nernst established the law thus: "It is impossible by any procedure to reach the isotherm T = 0 in a finite number of steps"
Thermodynamic processes
In the concept of thermodynamics, processes are the changes that take place in a system and that take it from a state of initial equilibrium to a state of final equilibrium. These are classified according to the variable that has been kept constant throughout the process.
A process may occur from melting ice, until ignition of air-fuel mixture to perform the movement of pistons in an engine of internal combustion.
There are three conditions that can vary in a thermodynamic system: temperature, volume, and pressure. Thermodynamic processes are studied in gases, since liquids are incompressible and volume changes do not occur. Also, due to high temperatures, liquids turn into gases. In solids, thermodynamic studies are not carried out because they are incompressible and there is no mechanical work on them.
Types of thermodynamic processes
These processes are classified according to their approach, to keep one of the variables constant, either temperature, pressure or volume. In addition, other criteria are applied, such as the exchange of energy and the modification of all its variables.
Isothermal process
Isothermal processes are all those in which the temperature of the system remains constant. This is done by working, so that the other variables (P and V) change over time.
Isobaric process
The isobaric process is one in which the pressure remains constant. Variation in temperature and volume will define its development. The volume can change freely when the temperature changes.
Isochoric processes
In isochoric processes the volume remains constant. It can also be considered as those in which the system does not generate any work (W = 0).
Basically, they are physical or chemical phenomena that are studied inside any container, whether with agitation or not.
Adiabatic process
The adiabatic process is that thermodynamic process in which there is no heat exchange from the system to the outside or in the opposite direction. Examples of this type of process are those that can be carried out in a thermos for drinks.
"> Loading…Examples of thermodynamic processes
- An example of the isochoric process: The volume of the gas is kept constant. When any type of temperature change occurs, it will be accompanied by a pressure change. As is the case with steam in a pressure cooker, it increases its pressure as it heats up.
- As an example of the Isothermal process: The gas temperature is kept constant. As the volume increases the pressure decreases. For example, a balloon in a vacuum making machine increases its volume as the vacuum is created.
- In relation to the adiabatic process: for example, the compression of the piston in a bicycle tire inflation pump, or the rapid decompression of the plunger of a syringe, previously compressing it with the outlet hole plugged.
