Thermodynamic Force

6 Key excerpts on "Thermodynamic Force"

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  eBook - ePub

  Molecular Driving Forces

  Statistical Thermodynamics in Biology, Chemistry, Physics, and Nanoscience

  • Ken Dill, Sarina Bromberg(Authors)
  • 2010(Publication Date)
  • Garland Science

    (Publisher)

  6 Thermodynamic Driving Forces Thermodynamics Is Two Laws and a Little Calculus

  Thermodynamics is a set of tools for reasoning about energies and entropies. It enables you to predict the tendencies of atoms and molecules to react; to bind, absorb, or partition; to dissolve or change phase; and to change their shapes or chemical bonds. The three basic tools of thermodynamics are the First Law for the conservation of energy (see Chapter 3 ), the maximum entropy principle, also called the Second Law of Thermodynamics (Chapters 2 and 5 ), and multivariate calculus (Chapter 4 ). In this chapter, we explore the definitions of the forces that act in material systems: pressure, the tendency to exchange volume; temperature, the tendency to exchange energy; and chemical potential, the tendency to exchange matter or to change its form.

  What Is a Thermodynamic System?

  A thermodynamic system is a collection of matter in any form, delineated from its surroundings by real or imaginary boundaries. The system may be a biological cell, the contents of a test tube, the gas in a piston, a thin film, or a can of soup. How you define a system depends on the problem that you want to solve. In thermodynamics, defining the boundaries is important, because boundaries determine what goes in or out. Much of thermodynamics is bookkeeping, accounting for energy or matter exchange across the boundaries or for volume changes. For a biochemical experiment, the boundary might be the walls of a test tube or a cell membrane. For a steam engine, the interior of the piston might be the most convenient definition of the system. The boundary need not be fixed in space. It need not even surround a fixed number of molecules. The system might contain subsystems, and the subsystems might also be delineated by real or imaginary boundaries. Systems are defined by the nature of their boundaries:

  OPEN SYSTEM . An open system can exchange energy, volume, and matter with its surroundings. The Earth and living organisms are open systems (see Figure 6.1

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  Advanced Thermodynamics

  • (Author)
  • 2014(Publication Date)
  • Library Press

    (Publisher)

  The temperature/entropy pair In a similar way, temperature differences drive changes in entropy, and their product is the energy transferred by heating. We should note that this is the only heat term, the other terms are essentially all various forms of work . The chemical potential/particle number pair The chemical potential is like a force which pushes an increase in particle number. In cases where there are a mixture of chemicals and phases, this is a useful concept. For example if a container holds water and water vapor, there will be a chemical potential (which is negative) for the liquid pushing water molecules into the vapor (evaporation) and a chemical potential for the vapor, pushing vapor molecules into the liquid (condensation). Only when these forces equilibrate is equilibrium obtained. ________________________ WORLD TECHNOLOGIES ________________________ Thermodynamic Potentials A thermodynamic potential is a scalar function used to represent the thermodynamic state of a system. The concept of thermodynamic potentials was introduced by Pierre Duhem in 1886. Josiah Willard Gibbs in his papers used the term fundamental functions . One main thermodynamic potential which has a physical interpretation is the internal energy, U. It is the energy of configuration of a given system of conservative forces (that is why it is a potential) and only has meaning with respect to a defined set of references (or data). Expressions for all other thermodynamic energy potentials are derivable via Legendre transforms from an expression for U. In thermodynamics, certain forces, such as gravity, are typically disregarded when formulating expressions for potentials. For example, while all the working fluid in a steam engine may have higher energy due to gravity while sitting on top of Mt.

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  Thermodynamics

  Processes and Applications

  • Jr. Logan, Jr., Earl Logan, Earl Logan Jr.(Authors)
  • 1999(Publication Date)
  • CRC Press

    (Publisher)

  Introduction I Chapter 1 Introduction 1.1 The Nature of Thermodynamics From physics we know that work occurs when a force acts through a distance. If a mass is elevated in a gravitational field, then a force must act through a distance against the weight of the object being raised, work is done and the body is said to possess an amount of potential energy equal to the work done. If the effect of a force is to accelerate a body, then the body is said to have kinetic energy equal to the work input. When two bodies have different temperatures, or degrees of hotness, and the bodies are in contact, then heat is said to flow from the hotter to the colder body. The thermodynamicist selects a portion of matter for study; this is the system. The chosen system can include a small collection of mat-ter, a group of objects, a machine or a stellar system; it can be very large or very small. The system receives or gives up work and heat, and the system collects and stores energy. Both work and heat are transitory forms of energy, i.e., energy that is trans-ferred to or from some material system; on the other hand, energy which is stored, e.g., potential energy or kinetic energy, is a prop-erty of the system. A primary goal of thermodynamics is to evaluate and relate work, heat and stored energy of systems. Thermodynamics deals with the conversion of heat into work or the use of work to produce a cooling or heating effect. We shall learn that these effects are brought about through the use of ther-modynamic cycles. If heat is converted into work in a cycle, then the cycle is a power cycle. On the other hand, if work is required to produce a cooling effect, the cycle is a refrigeration cycle. 2 Chapter 1 The term cycle is used to describe an ordered series of proc-esses through which a substance is made to pass in order to pro-duce the desired effect, e.g., refrigeration or work.

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  Terrestrial Biosphere-Atmosphere Fluxes

  • Russell Monson, Dennis Baldocchi(Authors)
  • 2014(Publication Date)
  • Cambridge University Press

    (Publisher)

  Potential energy is how we define the capacity for components in a natural system to do work. Potential energy exists in a thermodynamic system that is in a state of disequilibrium; in contrast, a system that is at equilibrium lacks potential energy, and therefore lacks the capacity to generate work on its surroundings or on other systems. Following an initial introduction to energy and work we will move to the thermodynamic basis for descriptions of temperature and pressure, emphasizing these concepts with regard to the earth system. Gradients in temperature and pressure represent two of the driving forces that determine transport processes in the atmosphere, and ultimately determine the direction and magnitude of energy exchange between the earth’ s surface and the atmosphere. We will use the concepts of thermal equilibrium and disequilibrium as paths to a discussion of sensible heat flux; the first biogeochemical flux we will consider in some detail. Finally, we will take up the topic of energy transfer through electromagnetic radiation. Electromagnetic radiation from the sun ultimately powers most of the biogeo- chemical transformations we will discuss in this book, both in terms of their chemical states and kinetic motions. 15 2.1 Thermodynamic systems and fluxes as thermodynamic processes Within the realm of biophysics, energy relations are often discussed with regard to a thermodynamic system, which has “boundaries” that separate it from the surroundings. In thermodynamic terms a system that can exchange heat and work with its surroundings, but not mass, is a closed system. It is important to note that a closed system is different than an isolated system. An isolated system does not exchange energy, work, or mass with its surroundings – it is indeed completely isolated! A system that exchanges heat, work, and mass with its surroundings is an open system.

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  Fundamentals of Chemical Engineering Thermodynamics, SI Edition

  • Kevin Dahm, Donald Visco(Authors)
  • 2014(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Chapter 3 introduces an energy balance equation that we will use extensively. In this equation, flow work is accounted for using the enthalpy ( H ), which is formally defined in Section 2.3.1. Throughout this book, the hat signifies a property expressed on a mass basis (e.g., specific volume) and the underline signifies a property expressed on a molar basis (e.g., molar volume V ). Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 28 Fundamentals of Chemical Engineering Thermodynamics 1.4.4 Kinetic Energy The connection between kinetic energy and the potential to do work is straight-forward; if an object is in motion, and there is a force opposing the motion, then work is being done. For example, consider a ball at the base of a hill (see Figure 1-24). It takes work to move the ball up the hill against the opposing force of gravity, and a person could supply this work by pushing the ball with his or her hand or foot. But if the ball, instead of being stationary at the bottom of the hill, is rolling along a flat surface toward the hill, then the ball rolls at least partway up the hill without any ex-ternal work required; the kinetic energy of the ball is equivalent to the work done by a person’s hand. Kinetic energy also can be transferred to other objects in the form of work, as when the moving billiard ball strikes the stationary one in Figure 1-9.

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  BTEC National Engineering

  • Mike Tooley, Lloyd Dingle(Authors)
  • 2010(Publication Date)
  • Routledge

    (Publisher)

  KEY POINT A thermodynamic system is essentially a thermodynamic substance surrounded by an identifiable boundary Thermodynamic systems Thermodynamic systems may be defined as particular amounts of a thermodynamic substance, normally compressible fluids such as vapours and gases, which are surrounded by an identifiable boundary. We are particularly interested in thermodynamic systems that involve working fluids (rather than solids) because these fluids enable the system to do work or have work done upon it. Only transient energies in the form of heat ( Q) and work ( W) can cross the system boundaries, and as a result there TYK 5.20 1. State the units and give the sign convention for heat flowing into and out of a system. 2. Write down the symbol for a quantity of heat energy. 3. Explain the nature of the two mechanisms of heat transfer by conduction. 4. What is the essential difference between heat transfer by convection and heat transfer by radiation? 5. With respect to engineering, why is the study of thermodynamics important? T e s t y o u r k n o w l e d g e TYK Mechanical Principles and Applications 427 UNIT 5 will be a change in the stored energy of the contained substance (working fluid). The property of a working fluid is an observable quantity, such as pressure, temperature, etc. The state of a working fluid may be defined by any two unique and independent properties. Boyle’s law defines the state of the fluid by specifying the independent thermodynamic properties of volume and pressure. A thermodynamic system must contain the following elements: ● a working fluid or substance, that is the matter, which may or may not cross the system boundaries, such as water, steam, air, etc. ● a heat source ● a cold body to promote heat flow and enable heat energy transfer ● system boundaries, which may or may not be fixed. Some of the more common properties (with units) that are used to define the state of the working matter within a thermodynamic system are shown in Table 5.4.

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