Technology & Engineering
Thermodynamic State
Thermodynamic state refers to the condition of a system as described by its temperature, pressure, and other relevant properties. It is a fundamental concept in thermodynamics, providing a snapshot of the system's physical state at a specific point in time. Understanding the thermodynamic state of a system is crucial for analyzing and predicting its behavior and energy interactions.
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8 Key excerpts on "Thermodynamic State"
No longer available |Learn more- David R. Gaskell, David E. Laughlin(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
Chapter 2 .The system may be a machine (heat engine) or a device (transducer) of interest to us. In the study of the thermodynamics of materials, the system is usually composed of matter, which is anything that has mass and occupies space. Matter has a given temperature, pressure, and chemical composition, as well as physical properties such as thermal expansion, compressibility, heat capacity, viscosity, and so on. A central aim of applied thermodynamics is the determination of the effect of the surroundings on the equilibrium state of a given system. Since the surroundings interacts with the system by transferring or receiving various forms of energy or matter with it, another focus of applied thermodynamics is the establishment of the relationships which exist between the equilibrium state of a given system and the influences which have been brought to bear on it.1.2THE CONCEPT OF STATEA fundamental concept in thermodynamics is that of the thermodynamic state . If it were possible to know the masses, velocities, positions, and all modes of motion (translational, rotational, etc.) of all of the constituent particles in a system, this knowledge would serve to describe the microscopic state of the system, which, in turn, would determine, in principle, all of the thermodynamic variables of the system that can be measured (energy, temperature, pressure, etc.). For systems with macroscopic dimensions, this would entail more than 1024 coordinates, which is clearly an impossible task. In the absence of such detailed knowledge as is required to determine the microscopic state of the system, classical thermodynamics begins with a consideration of the variables of the system, which, when determined, completely define the macroscopic state of the system; that is, when all of the thermodynamic variables are fixed, then the macroscopic state of the system is fixed and is said to be in equilibrium. It is found that when the values of a small number of thermodynamic variables are fixed, the values of the rest of the thermodynamic variables are also fixed. Indeed, when a simple system such as a given quantity of a substance of fixed composition is being considered, the fixing of the values of two of the thermodynamic variables fixes the values of the rest of the thermodynamic variables. Thus, only two thermodynamic variables are independent, which, consequently, are called the independent thermodynamic variables of the system. All of the other variables are dependent variables . The Thermodynamic State of such a system is thus uniquely determined when the values of the two independent variables are fixed. This has been called the Duhem*postulate
eBook - PDFPhase Equilibria, Phase Diagrams and Phase Transformations
Their Thermodynamic Basis
- Mats Hillert(Author)
- 2007(Publication Date)
- Cambridge University Press(Publisher)
1 Basic concepts of thermodynamics 1.1 External state variables Thermodynamics is concerned with the state of a system when left alone, and when inter-acting with the surroundings. By ‘system’ we shall mean any portion of the world that can be defined for consideration of the changes that may occur under varying conditions. The system may be separated from the surroundings by a real or imaginary wall. The proper-ties of the wall determine how the system may interact with the surroundings. The wall itself will not usually be regarded as part of the system but rather as part of the sur-roundings. We shall first consider two kinds of interactions, thermal and mechanical, and we may regard the name ‘thermodynamics’ as an indication that these interactions are of main interest. Secondly, we shall introduce interactions by exchange of matter in the form of chemical species. The name ‘thermochemistry’ is sometimes used as an indication of such applications. The term ‘thermophysical properties’ is sometimes used for thermodynamic properties which do not primarily involve changes in the content of various chemical species, e.g. heat capacity, thermal expansivity and compressibility. One might imagine that the content of matter in the system could be varied in a number of ways equal to the number of species. However, species may react with each other inside the system. It is thus convenient instead to define a set of independent components , the change of which can accomplish all possible variations of the content. By denoting the number of independent components as c and also considering thermal and mechanical interactions with the surroundings, we find by definition that the state of the system may vary in c + 2 independent ways. For metallic systems it is usually most convenient to regard the elements as the independent components. For systems with covalent bonds it may sometimes be convenient to regard a very stable molecular species as a component.
- Carlo Di Castro, Roberto Raimondi(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
1 Thermodynamics: a brief overview Thermodynamics is a phenomenological theory based on empirical observations. The thermodynamic laws are a coherent account of the experimental analysis and provide a universally valid description of the behavior of macroscopic systems without referring to their detailed structure. In this chapter we introduce thermodynamics as a prerequisite scenario for statistical mechanics and we do not give an extended exposition of the theory, but only recall the basic concepts as an introduction to the statistical approach. 1 1.1 Equilibrium states and the empirical temperature A thermodynamic system is any portion of matter, solid, liquid, mixtures, . . . , which can be described in terms of a small number of parameters, the macroscopic thermodynamic variables, as for example the pressure P and the volume V for a fluid or the magnetic moment and the magnetic field for a paramagnet. These variables are called extensive or intensive, depending whether their value does or does not depend on the amount of matter present in the system. Energy, volume and magnetization are extensive variables, whereas pressure, temperature and magnetic field are intensive. Thermodynamics deals with macroscopic properties of macro-systems at equilibrium. A thermodynamic equilibrium state must then be characterized as a macroscopic phenomenon defined via macroscopic variables. A system is in equilibrium if the values of the observ- ables we take into consideration and of the parameters describing its state do not change with time. The thermodynamic equilibrium is never fully static. The characterization of a Thermodynamic State depends on the observation time, usually at least of the order of fractions of a second, which in any case must always be much longer than any characteristic time scale of the molecular motion (∼10 −11 s). We use a simple example of common experience to illustrate this point.
eBook - PDF- Marc J. Assael, William A. Wakeham, Anthony R. H. Goodwin, Stefan Will, Michael Stamatoudis(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
A system is characterized both by its contents and the system boundary; the latter in the end is always virtual. For example, if one considers a container with a rigid enclosure, the boundary of the system is set in a way to include all the material inside but to exclude the walls. Especially in engineering applications, a careful and advantageous choice of the system boundary is of enormous importance; defining the right system boundary may considerably ease setting up energy and mass balances, for example. 1.3.2 What Is a State? The state of a system is defined by specifying a number of thermodynamic vari-ables for the system under study. In principle, these could be any or all of the measurable physical properties of a system. Fortunately, not all of the variables or properties need to be specified to define the state of the system because only a few can be varied independently; the exact number of independent variables depends on the system but rarely exceeds five. The exact choice of the inde-pendent variables for a system is a matter of convenience, but pressure and Definitions and the 1 st Law of Thermodynamics 4 temperature are often included within them. As an illustration of this point, if the temperature and pressure of a pure gas are specified then the density of the gas takes a value (dependent variable) that is determined. The general rule for calculating the number of independent variables for a system at equi-librium is given by the phase rule that will be introduced and discussed in Question 4.1.1. 1.3.3 What Are the Types of Property: Extensive and Intensive? For a system that can be divided into parts any property of the system that is the sum of the property of the parts is extensive. For example, the mass of the system is the sum of the mass of all parts into which it is divided.
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
2 Thermodynamics: Preliminary Concepts and Definitions Chapter Objectives • To briefly introduce the subject of thermodynamics. • To provide precise definitions of some of the working terms used in a study of thermodynamics. • To consider the dimensions and units that pertain to thermodynamics. • To examine density and its related properties. • To define pressure and consider how it is measured. • To define temperature and to present the zeroth law of thermodynamics. • To outline a problem-solving methodology. 2.1 The Study of Thermodynamics When most people think about thermodynamics, they think about the transfer of energy and the utilization of such energy transfer for the useful production of work. This often leads many engineering students in fields such as computer science and electrical or civil engineering to wonder why this particular subject is relevant to them. In reality, thermody-namics deals with much more than the study of heat or energy transfer and the development of work. Indeed, it deals with virtually all aspects of our lives, from the combustion pro-cesses that run our automobiles and produce our electric power in power plants to the refrigeration cycles that cool our beer, from the cryogenic pumping of liquids and gases in space to the distillation processes used to produce the gasoline that runs our automobiles. Thermodynamics is important to electrical engineers so that they can better understand that the limiting factor in the microminiaturization of electronic components is the rejec-tion of heat. It is important to civil engineers because a knowledge of thermal expansion and thermal stresses is requisite to the design of structures and to the computer scien-tists who need to thoroughly understand the systems that they are trying to model and develop.
eBook - PDF- Donald Olander(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
• The isolated system : Thermodynamics reserves a special name for a boundary that is both adiabatic and rigid, and is not penetrated by rotating shafts, electrical wires or other devices that could transmit non-pV forms of work. A system protected by such a boundary is called isolated . It would appear that a system that cannot be influenced by its surroundings is of little practical interest. This is indeed so. However, the isolated system occupies a hallowed niche in thermodynamic theory because it provides one of the simplest ways of elucidating some of its more esoteric features, such as equilibrium, spontaneity of change and entropy. • Mass transmission : The mass-transmitting capabilities of a system bound-ary possess limits analogous to those of heat and work transmissibility. Concepts and Definitions 15 The boundaries of the closed system are impervious to all matter; the material inside a closed system retains its elemental identity during passage of heat and/or work across its boundaries. However, the system’s molecular composition may change by chemical reaction. In an open system, matter flows across inlets and outlets in the boundary (Figure 1.9). At steady state, the quantity of matter in an open system is constant. In contrast to a closed system, gradients of thermodynamic properties are permitted in open systems (e.g., the pressure decrease through a turbine). 1.5 THERMODYNAMIC PROCESSES A thermodynamic process is the act of changing the state of a system. The state of the system is defined by a few properties such as temperature, pressure, etc. The process may occur spontaneously, such as the reaction of H 2 and O 2 to form H 2 O, or it may be induced as a result of the interchange of heat and work with the surroundings. We are always interested in the initial and final states of a process, and often in the path followed between these two states. However, thermodynamics is blind to the rate of the process.
eBook - PDFThermodynamics of Surfaces and Interfaces
Concepts in Inorganic Materials
- Gerald H. Meier(Author)
- 2014(Publication Date)
- Cambridge University Press(Publisher)
1 Summary of basic thermodynamic concepts This chapter provides a summary of the three laws of thermodynamics and the important defined functions and relations for applying these laws to materials systems. It is assumed that the reader has completed an introductory course on thermodynamics. The purpose of this chapter is to bring the reader back “up to speed”. An extensive reference list of thermodynamic data sources is also provided. 1.1 Basic thermodynamics The subject of thermodynamics is based on three empirical laws and their application, generally through the use of specially defined func- tions. A summary of the three laws and the various defined functions follows. The reader is referred to one of the many comprehensive texts on thermodynamics for a more detailed treatment [1–4]. 1.1.1 Extensive and molar properties of a thermodynamic system The properties (state functions) which refer to the entire system and, therefore, are dependent on size (e.g. mass, volume) are termed extensive and may be represented by a generic quantity, Q . Those properties which are independent of the size of the system (e.g. temperature, pressure) are termed intensive. The ratio of any two extensive properties becomes an intensive property. A particularly useful quantity of this type arises when a particular Q is divided by the number of moles of material in 1 2 summary of basic thermodynamic concepts the system, yielding a molar quantity, Q: Q = Q n (1.1) For example, V = V / n is the molar volume of the system. The contribution of each component to an extensive property of the system under isobaric and isothermal conditions is described by the partial molar quantities, ¯ Q i : ¯ Q i ≡ ∂ Q ∂ n i T , P,n j (1.2) where n i represents the number of moles of component i and n j represents the numbers of moles of the other components in the system. ¯ Q i is that part of Q which is contributed by one mole of component i.
eBook - PDFStatistical and Thermal Physics
With Computer Applications, Second Edition
- Harvey Gould, Jan Tobochnik(Authors)
- 2021(Publication Date)
- Princeton University Press(Publisher)
2 The nature of thermodynamics is summarized in the song “First and Second Law” by Michael Flanders and Donald Swann. 2.3 THERMODYNAMIC EQUILIBRIUM • 31 Surroundings Boundary System Figure 2.1. Schematic of a thermodynamic system. Thermodynamics describes the properties of macroscopic systems without appeal to the nature of their microscopic constituents. So why bother introducing thermo-dynamics as a subject in its own right, when we could more easily introduce energy and entropy from microscopic considerations? Besides the intellectual challenge, an important reason is that the way of thinking required by thermodynamics can be applied in other contexts where the microscopic properties of the system are poorly understood or very complex. However, there is no need to forget what we learned in Chapter 1. You are also encouraged to jump ahead, especially to Chapter 4, where the nature of entropy is introduced from first principles. 2.2 The System The first step in applying thermodynamics is to select the part of the universe of interest. This part of the universe is called the system . The system is anything that we wish to consider and is defined by a closed surface called the boundary (see Figure 2.1). The boundary may be real or imaginary and may or may not be fixed in shape or size. The system might be as obvious as a block of steel, water in a container, or the gas in a balloon. Or the system might be defined by an imaginary fixed boundary within a flowing liquid. The surroundings are the rest of the universe that can in any significant way affect or be affected by the system. If an ice cube is placed in a glass of water, we might take the ice to be the system and the water to be the surroundings. In this example we usually ignore the interaction of the ice cube with the air in the room and the interaction of the glass with the table on which the glass is set.
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