Thermodynamic system

A thermodynamic system is a group of material and/or radiative contents. Its properties may be described by thermodynamic state variables such as temperature, entropy, internal energy, and pressure.Thermodynamic equilibrium is characterized by absence of flow of mass or energy. Equilibrium thermodynamics, as a subject in physics, considers macroscopic bodies of matter and energy in states of internal thermodynamic equilibrium. It uses the concept of thermodynamic processes, by which bodies pass from one equilibrium state to another by transfer of matter and energy between them. The term 'thermodynamic system' is used to refer to bodies of matter and energy in the special context of thermodynamics. The possible equilibria between bodies are determined by the physical properties of the walls that separate the bodies. Equilibrium thermodynamics in general does not measure time. Equilibrium thermodynamics is a relatively simple and well settled subject. One reason for this is the existence of a well defined physical quantity called 'the entropy of a body'.The first to create the concept of a thermodynamic system was the French physicist Sadi Carnot whose 1824 Reflections on the Motive Power of Fire studied what he called the working substance, e.g., typically a body of water vapor, in steam engines, in regards to the system's ability to do work when heat is applied to it. The working substance could be put in contact with either a heat reservoir (a boiler), a cold reservoir (a stream of cold water), or a piston (to which the working body could do work by pushing on it). In 1850, the German physicist Rudolf Clausius generalized this picture to include the concept of the surroundings, and began referring to the system as a 'working body'. In his 1850 manuscript On the Motive Power of Fire, Clausius wrote:At thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems not in equilibrium. In some cases, when analyzing a thermodynamic process, one can assume that each intermediate state in the process is at equilibrium. This considerably simplifies the analysis.impermeable to matterimpermeable to matterA system is enclosed by walls that bound it and connect it to its surroundings. Often a wall restricts passage across it by some form of matter or energy, making the connection indirect. Sometimes a wall is no more than an imaginary two-dimensional closed surface through which the connection to the surroundings is direct.The system is the part of the universe being studied, while the surroundings is the remainder of the universe that lies outside the boundaries of the system. It is also known as the environment, and the reservoir. Depending on the type of system, it may interact with the system by exchanging mass, energy (including heat and work), momentum, electric charge, or other conserved properties. The environment is ignored in analysis of the system, except in regards to these interactions.In a closed system, no mass may be transferred in or out of the system boundaries. The system always contains the same amount of matter, but heat and work can be exchanged across the boundary of the system. Whether a system can exchange heat, work, or both is dependent on the property of its boundary.An isolated system is more restrictive than a closed system as it does not interact with its surroundings in any way. Mass and energy remains constant within the system, and no energy or mass transfer takes place across the boundary. As time passes in an isolated system, internal differences in the system tend to even out and pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion is in a state of thermodynamic equilibrium.For a thermodynamic process, the precise physical properties of the walls and surroundings of the system are important, because they determine the possible processes.In an open system, there is an exchange of energy and matter between the system and the surroundings.The presence of reactants in an open beaker is an example of an open system.Here the boundaray is an imaginary surface enclosing the beaker and reactants. It is named closed, if borders are impenetrable for substance, but allow transit of energy in the form of heat, and isolated, if there is no exchange of heat and substances. The open system cannot exist in the equilibrium state. To describe deviation of the thermodynamic system from equilibrium, in addition to constitutive variables that was described above, a set of internal variables ξ 1 , ξ 2 , … {displaystyle xi _{1},xi _{2},ldots } that are called internal variables have been introduced. The equilibrium state is considered to be stable. and the main property of the internal variables, as measures of non-equilibrium of the system, is their trending to disappear; the local law of disappearing can be written as relaxation equation for each internal variable d ξ i d t = − 1 τ i ( ξ i − ξ i ( 0 ) ) , i = 1 , 2 , … , {displaystyle {frac {dxi _{i}}{dt}}=-{frac {1}{ au _{i}}},left(xi _{i}-xi _{i}^{(0)} ight),quad i=1,,2,ldots ,} (1) T d S = Δ Q − ∑ j Ξ j Δ ξ j + ∑ α = 1 k μ α Δ N α . {displaystyle T,dS=Delta Q-sum _{j},Xi _{j},Delta xi _{j}+sum _{alpha =1}^{k},mu _{alpha },Delta N_{alpha }.} (1)An adiabatic system is the one which doesn't allow any heat to be transferred into or out of the system. The P V γ = c o n s t a n t {displaystyle PV^{gamma }=constant} equation is only valid for an adiabatic system which is also undergoing a reversible process provided it is a closed system having an ideal gas. If it fails to satisfy any of these conditions then only d Q = 0 {displaystyle dQ=0} is true and it cannot be represented in an equation like P V γ = c o n s t a n t {displaystyle PV^{gamma }=constant} .