Isolated system

Last updated

Properties of Isolated, closed, and open systems in exchanging energy and matter. Diagram Systems.png
Properties of Isolated, closed, and open systems in exchanging energy and matter.

In physical science, an isolated system is either of the following:

Contents

  1. a physical system so far removed from other systems that it does not interact with them.
  2. a thermodynamic system enclosed by rigid immovable walls through which neither mass nor energy can pass.

Though subject internally to its own gravity, an isolated system is usually taken to be outside the reach of external gravitational and other long-range forces.

This can be contrasted with what (in the more common terminology used in thermodynamics) is called a closed system, being enclosed by selective walls through which energy can pass as heat or work, but not matter; and with an open system, which both matter and energy can enter or exit, though it may have variously impermeable walls in parts of its boundaries.

An isolated system obeys the conservation law that its total energy–mass stays constant. Most often, in thermodynamics, mass and energy are treated as separately conserved.

Because of the requirement of enclosure, and the near ubiquity of gravity, strictly and ideally isolated systems do not actually occur in experiments or in nature. Though very useful, they are strictly hypothetical. [1] [2] [3]

Classical thermodynamics is usually presented as postulating the existence of isolated systems. It is also usually presented as the fruit of experience. Obviously, no experience has been reported of an ideally isolated system.

It is, however, the fruit of experience that some physical systems, including isolated ones, do seem to reach their own states of internal thermodynamic equilibrium. Classical thermodynamics postulates the existence of systems in their own states of internal thermodynamic equilibrium. This postulate is a very useful idealization.

In the attempt to explain the idea of a gradual approach to thermodynamic equilibrium after a thermodynamic operation, with entropy increasing according to the second law of thermodynamics, Boltzmann’s H-theorem used equations, which assumed a system (for example, a gas) was isolated. That is, all the mechanical degrees of freedom could be specified, treating the enclosing walls simply as mirror boundary conditions. This led to Loschmidt's paradox. If, however, the stochastic behavior of the molecules and thermal radiation in real enclosing walls is considered, then the system is in effect in a heat bath. Then Boltzmann’s assumption of molecular chaos can be justified.

The concept of an isolated system can serve as a useful model approximating many real-world situations. It is an acceptable idealization used in constructing mathematical models of certain natural phenomena; e.g., the planets in the Solar System, and the proton and electron in a hydrogen atom are often treated as isolated systems. But, from time to time, a hydrogen atom will interact with electromagnetic radiation and go to an excited state.

Radiative isolation

For radiative isolation, the walls should be perfectly conductive, so as to perfectly reflect the radiation within the cavity, as for example imagined by Planck.

He was considering the internal thermal radiative equilibrium of a thermodynamic system in a cavity initially devoid of substance. He did not mention what he imagined to surround his perfectly reflective and thus perfectly conductive walls. Presumably, since they are perfectly reflective, they isolate the cavity from any external electromagnetic effect. Planck held that for radiative equilibrium within the isolated cavity, it needed to have added to its interior a speck of carbon. [4] [5] [6]

If the cavity with perfectly reflective walls contains enough radiative energy to sustain a temperature of cosmological magnitude, then the speck of carbon is not needed because the radiation generates particles of substance, such as for example electron-positron pairs, and thereby reaches thermodynamic equilibrium.

A different approach is taken by Balian. For quantizing the radiation in the cavity, he imagines his radiatively isolating walls to be perfectly conductive. Though he does not mention mass outside, and it seems from his context that he intends the reader to suppose the interior of the cavity to be devoid of mass, he does imagine that some factor causes currents in the walls. If that factor is internal to the cavity, it can be only the radiation, which would thereby be perfectly reflected. For the thermal equilibrium problem, however, he considers walls that contain charged particles that interact with the radiation inside the cavity; such cavities are of course not isolated, but may be regarded as in a heat bath. [7]

See also

Related Research Articles

In physics, statistical mechanics is a mathematical framework that applies statistical methods and probability theory to large assemblies of microscopic entities. It does not assume or postulate any natural laws, but explains the macroscopic behavior of nature from the behavior of such ensembles.

<span class="mw-page-title-main">Thermodynamics</span> Physics of heat, work, and temperature

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.

Black body Idealized physical body that absorbs all incident electromagnetic radiation

A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body also emits black-body radiation. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions."

<span class="mw-page-title-main">Second law of thermodynamics</span> Physical law regarding entropy and the flow of heat

The second law of thermodynamics is a physical law based on universal experience concerning heat and energy interconversions. One simple statement of the law is that heat always moves "downhill", that is, from hotter objects to colder objects, unless energy is supplied to reverse the direction of heat flow. Another definition is: "Not all heat energy can be converted into work in a cyclic process."

First law of thermodynamics Law of thermodynamics distinguishing heat, work, and matter transfers

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing three kinds of transfer of energy, as heat, as thermodynamic work, and as energy associated with matter transfer, and relating them to a function of a body's state, called internal energy.

Heat transfer Transport of thermal energy in physical systems

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

Thermal radiation Electromagnetic radiation generated by the thermal motion of particles

Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material is converted to electromagnetic radiation. All matter with a temperature greater than absolute zero emits thermal radiation. At room temperature, most of the emission is in the infrared (IR) spectrum. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.

In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T, when there is no net flow of matter or energy between the body and its environment.

<span class="mw-page-title-main">Zeroth law of thermodynamics</span> Physical law for definition of temperature

The zeroth law of thermodynamics is one of the four principle laws of thermodynamics. It provides an independent definition of temperature without reference to entropy, which is defined in the second law. The law was established by Ralph H. Fowler in the 1930s, long after the first, second, and third laws were widely recognized.

Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium there are no net macroscopic flows of matter or of energy, within a system or between systems. In a system that is in its own state of internal thermodynamic equilibrium, no macroscopic change occurs.

<span class="mw-page-title-main">Thermodynamic system</span> Body of matter in a state of internal equilibrium

A thermodynamic system is a body of matter and/or radiation, confined in space by walls, with defined permeabilities, which separate it from its surroundings. The surroundings may include other thermodynamic systems, or physical systems that are not thermodynamic systems. A wall of a thermodynamic system may be purely notional, when it is described as being 'permeable' to all matter, all radiation, and all forces. A state of a thermodynamic system can be fully described in several different ways, by several different sets of thermodynamic state variables.

Thermal equilibrium State of no net thermal energy flow between two connected systems

Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in thermal equilibrium with itself if the temperature within the system is spatially uniform and temporally constant.

Kirchhoffs law of thermal radiation Law of wavelength-specific emission and absorption

In heat transfer, Kirchhoff's law of thermal radiation refers to wavelength-specific radiative emission and absorption by a material body in thermodynamic equilibrium, including radiative exchange equilibrium.

Black-body radiation Thermal electromagnetic radiation

Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body. It has a specific, continuous spectrum of wavelengths, inversely related to intensity, that depend only on the body's temperature, which is assumed, for the sake of calculations and theory, to be uniform and constant.

<span class="mw-page-title-main">Laws of thermodynamics</span> Axiomatic basis of thermodynamics

The laws of thermodynamics define a group of physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems in thermodynamic equilibrium. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. They state empirical facts that form a basis of precluding the possibility of certain phenomena, such as perpetual motion. In addition to their use in thermodynamics, they are important fundamental laws of physics in general, and are applicable in other natural sciences.

History of thermodynamics

The history of thermodynamics is a fundamental strand in the history of physics, the history of chemistry, and the history of science in general. Owing to the relevance of thermodynamics in much of science and technology, its history is finely woven with the developments of classical mechanics, quantum mechanics, magnetism, and chemical kinetics, to more distant applied fields such as meteorology, information theory, and biology (physiology), and to technological developments such as the steam engine, internal combustion engine, cryogenics and electricity generation. The development of thermodynamics both drove and was driven by atomic theory. It also, albeit in a subtle manner, motivated new directions in probability and statistics; see, for example, the timeline of thermodynamics.

Thermodynamic state Quantifiable conditions of a thermodynamic system at a specific time

In thermodynamics, a thermodynamic state of a system is its condition at a specific time; that is, fully identified by values of a suitable set of parameters known as state variables, state parameters or thermodynamic variables. Once such a set of values of thermodynamic variables has been specified for a system, the values of all thermodynamic properties of the system are uniquely determined. Usually, by default, a thermodynamic state is taken to be one of thermodynamic equilibrium. This means that the state is not merely the condition of the system at a specific time, but that the condition is the same, unchanging, over an indefinitely long duration of time.

<span class="mw-page-title-main">Temperature</span> Physical quantity that expresses hot and cold

Temperature is a physical quantity that expresses the hotness of matter or radiation.

In thermodynamics, an adiabatic wall between two thermodynamic systems does not allow heat or chemical substances to pass across it, in other words there is no heat transfer nor mass transfer.

In thermodynamics, a diathermal wall between two thermodynamic systems allows heat transfer but do not allow transfer of matter across it.

References

  1. Thermodynamics of Spontaneous and Non-Spontaneous Processes; I. M. Kolesnikov et al, pg 136 – at https://books.google.com/books?id=2RzE2pCfijYC&pg=PA3
  2. A System and Its Surroundings; UC Davis ChemWiki, by University of California - Davis, at http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/A_System_And_Its_Surroundings#Isolated_System
  3. Hyperphysics, by the Department of Physics and Astronomy of Georgia State University; at http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html#isosys
  4. Planck, M. (1914). The Theory of Heat Radiation, second edition translated by Masius, P. Blakiston's Son & Co., Philadelphia, p. 43.
  5. Fowler, R.H. (1929). Statistical Mechanics: the Theory of the Properties of Matter in Equilibrium, Cambridge University Press, London, p. 74.
  6. Landsberg, P.T. (1978). Thermodynamics and Statistical Mechanics, Oxford University Press, Oxford UK, ISBN   0-19-851142-6, pp. 208–209.
  7. Balian, R., (1982). From Microphysics to Macrophysics: Methods and Applications of Statistical Physics, translated by D. ter Haar, volume 2, Springer, ISBN   978-3-540-45478-6, pp. 203, 215.