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Thermodynamics

2007 Schools Wikipedia Selection. Related subjects: General Physics

   Thermodynamics (from the Greek thermos meaning heat and dynamics
   meaning power) is a branch of physics that studies the effects of
   changes in temperature, pressure, and volume on physical systems at the
   macroscopic scale by analyzing the collective motion of their particles
   using statistics. Roughly, heat means "energy in transit" and dynamics
   relates to "movement"; thus, in essence thermodynamics studies the
   movement of energy and how energy instills movement. Historically,
   thermodynamics developed out of the need to increase the efficiency of
   early steam engines.
   Typical thermodynamic system - heat moves from hot (boiler) to cold
   (condenser) and work is extracted.
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   Typical thermodynamic system - heat moves from hot (boiler) to cold
   (condenser) and work is extracted.

   The starting point for most thermodynamic considerations are the laws
   of thermodynamics, which postulate that energy can be exchanged between
   physical systems as heat or work. They also postulate the existence of
   a quantity named entropy, which can be defined for any system. In
   thermodynamics, interactions between large ensembles of objects are
   studied and categorized. Central to this are the concepts of system and
   surroundings. A system is composed of particles, whose average motions
   define its properties, which in turn are related to one another through
   equations of state. Properties can be combined to express internal
   energy and thermodynamic potentials, which are useful for determining
   conditions for equilibrium and spontaneous processes.

   With these tools, thermodynamics describes how systems respond to
   changes in their surroundings. This can be applied to a wide variety of
   topics in science and engineering, such as engines, phase transitions,
   chemical reactions, transport phenomena, and even black holes. The
   results of thermodynamics are essential for other fields of physics and
   for chemistry, chemical engineering, cell biology, biomedical
   engineering, and materials science to name a few.

History

   Sadi Carnot (1796-1832): the "father" of thermodynamics
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   Sadi Carnot (1796-1832): the "father" of thermodynamics

   A short history of thermodynamics begins with the German scientist Otto
   von Guericke who in 1650 built and designed the world's first vacuum
   pump and created the world's first ever vacuum (known as the Magdeburg
   hemispheres). He was driven to make a vacuum in order to disprove
   Aristotle's long-held supposition that 'nature abhors a vacuum'.
   Shortly thereafter, Irish physicist and chemist Robert Boyle had
   learned of Guericke's designs and in 1656, in coordination with English
   scientist Robert Hooke, built an air pump. Using this pump, Boyle and
   Hooke noticed the pressure-temperature-volume correlation. In time,
   Boyle's Law was formulated, which states that pressure and volume are
   inversely proportional. Then, in 1679, based on these concepts, an
   associate of Boyle's named Denis Papin built a bone digester, which was
   a closed vessel with a tightly fitting lid that confined steam until a
   high pressure was generated.

   Later designs implemented a steam release valve that kept the machine
   from exploding. By watching the valve rhythmically move up and down,
   Papin conceived of the idea of a piston and cylinder engine. He did
   not, however, follow through with his design. Nevertheless, in 1697,
   based on Papin's designs, engineer Thomas Savery built the first
   engine. Although these early engines were crude and inefficient, they
   attracted the attention of the leading scientists of the time. One such
   scientist was Sadi Carnot, the "father of thermodynamics", who in 1824
   published “Reflections on the Motive Power of Fire”, a discourse on
   heat, power, and engine efficiency. The paper outlined the basic
   energetic relations between the Carnot engine, the Carnot cycle, and
   Motive power. This marks the start of thermodynamics as a modern
   science.

   The term thermodynamics was coined by James Joule in 1858 to designate
   the science of relations between heat and power. By 1849,
   "thermo-dynamics", as a functional term, was used in William Thomson's
   paper An Account of Carnot's Theory of the Motive Power of Heat. The
   first thermodynamic textbook was written in 1859 by William Rankine, a
   civil and mechanical engineering professor at the University of
   Glasgow.

Classical thermodynamics

   Classical thermodynamics is the original early 1800s variation of
   thermodynamics concerned with thermodynamic states, and properties as
   energy, work, and heat, and with the laws of thermodynamics, all
   lacking an atomic interpretation. In precursory form, classical
   thermodynamics derives from physicist Robert Boyle’s 1662 postulate
   that the pressure P of a given quantity of gas varies inversely as its
   volume V at constant temperature; i.e. in equation form: PV = k, a
   constant. From here, a semblance of a thermo-science began to develop
   with the construction of the first successful atmospheric steam engines
   in England by Thomas Savery in 1697 and Thomas Newcomen in 1712. The
   first and second laws of thermodynamics emerged simultaneously in the
   1850s, primarily out of the works of William Rankine, Rudolf Clausius,
   and William Thomson (Lord Kelvin).

Statistical thermodynamics

   With the development of atomic and molecular theories in the late 19th
   century, thermodynamics was given a molecular interpretation. This
   field is called statistical thermodynamics, which can be thought of as
   a bridge between macroscopic and microscopic properties of systems.
   Essentially, statistical thermodynamics is an approach to
   thermodynamics situated upon statistical mechanics, which focuses on
   the derivation of macroscopic results from first principles. It can be
   opposed to its historical predecessor phenomenological thermodynamics,
   which gives scientific descriptions of phenomena with avoidance of
   microscopic details. The statistical approach is to derive all
   macroscopic properties (temperature, volume, pressure, energy, entropy,
   etc.) from the properties of moving constituent particles and the
   interactions between them (including quantum phenomena). It was found
   to be very successful and thus is commonly used.

Chemical thermodynamics

   Chemical thermodynamics is the study of the interrelation of heat with
   chemical reactions or with a physical change of state within the
   confines of the laws of thermodynamics. During the years 1873-76 the
   American mathematical physicist Willard Gibbs published a series of
   three papers, the most famous being On the Equilibrium of Heterogeneous
   Substances, in which he showed how thermodynamic processes could be
   graphically analyzed, by studying the energy, entropy, volume,
   temperature and pressure of the thermodynamic system, in such a manner
   to determine if a process would occur spontaneously. During the early
   20th century, chemists such as Gilbert Lewis, Merle Randall, and E. A.
   Guggenheim began to apply the mathematical methods of Gibbs to the
   analysis of chemical processes.

Thermodynamic systems

   Enlarge

   An important concept in thermodynamics is the “system”. A system is the
   region of the universe under study. A system is separated from the
   remainder of the universe by a boundary which may be imaginary or not,
   but which by convention delimits a finite volume. The possible
   exchanges of work, heat, or matter between the system and the
   surroundings take place across this boundary. There are five dominant
   classes of systems:
    1. Isolated Systems – matter and energy may not cross the boundary.
    2. Adiabatic Systems – heat may not cross the boundary.
    3. Diathermic Systems - heat may cross boundary.
    4. Closed Systems – matter may not cross the boundary.
    5. Open Systems – heat, work, and matter may cross the boundary.

   For isolated systems, as time goes by, internal differences in the
   system tend to even out; pressures and temperatures tend to equalize,
   as do density differences. A system in which all equalizing processes
   have gone practically to completion, is considered to be in a state of
   thermodynamic equilibrium.

   In thermodynamic equilibrium, a system's properties are, by definition,
   unchanging in time. Systems in equilibrium are much simpler and easier
   to understand than systems which are not in equilibrium. Often, when
   analyzing a thermodynamic process, it can be assumed that each
   intermediate state in the process is at equilibrium. This will also
   considerably simplify the situation. Thermodynamic processes which
   develop so slowly as to allow each intermediate step to be an
   equilibrium state are said to be reversible processes.

Thermodynamic parameters

   The central concept of thermodynamics is that of energy, the ability to
   do work. As stipulated by the first law, the total energy of the system
   and its surroundings is conserved. It may be transferred into a body by
   heating, compression, or addition of matter, and extracted from a body
   either by cooling, expansion, or extraction of matter. For comparison,
   in mechanics, energy transfer results from a force which causes
   displacement, the product of the two being the amount of energy
   transferred. In a similar way, thermodynamic systems can be thought of
   as transferring energy as the result of a generalized force causing a
   generalized displacement, with the product of the two being the amount
   of energy transferred. These thermodynamic force-displacement pairs are
   known as conjugate variables. The most common conjugate thermodynamic
   variables are pressure-volume (mechanical parameters),
   temperature-entropy (thermal parameters), and chemical
   potential-particle number (material parameters).

Thermodynamic instruments

   There are two types of thermodynamic instruments, the meter and the
   reservoir. A thermodynamic meter is any device which measures any
   parameter of a thermodynamic system. In some cases, the thermodynamic
   parameter is actually defined in terms of an idealized measuring
   instrument. For example, the zeroth law states that if two bodies are
   in thermal equilibrium with a third body, they are also in thermal
   equilibrium with each other. This principle, as noted by James Maxwell
   in 1872, asserts that it is possible to measure temperature. An
   idealized thermometer is a sample of an ideal gas at constant pressure.
   From the ideal gas law PV=nRT, the volume of such a sample can be used
   as an indicator of temperature; in this manner it defines temperature.
   Although pressure is defined mechanically, a pressure-measuring device,
   called a barometer may also be constructed from a sample of an ideal
   gas held at a constant temperature. A calorimeter is a device which is
   used to measure and define the internal energy of a system.

   A thermodynamic reservoir is a system which is so large that it does
   not appreciably alter its state parameters when brought into contact
   with the test system. It is used to impose a particular value of a
   state parameter upon the system. For example, a pressure reservoir is a
   system at a particular pressure, which imposes that pressure upon any
   test system that it is mechanically connected to. The earth's
   atmosphere is often used as a pressure reservoir.

   It is important that these two types of instruments are distinct. A
   meter does not perform its task accurately if it behaves like a
   reservoir of the state variable it is trying to measure. If, for
   example, a thermometer, were to act as a temperature reservoir it would
   alter the temperature of the system being measured, and the reading
   would be incorrect. Ideal meters have no effect on the state variables
   of the system they are measuring.

Thermodynamic states

   When a system is at equilibrium under a given set of conditions, it is
   said to be in a definite state. The state of the system can be
   described by a number of intensive variables and extensive variables.
   The properties of the system can be described by an equation of state
   which specifies the relationship between these variables. State may be
   thought of as the instantaneous quantitative description of a system
   with a set number of variables held constant.

Thermodynamic processes

   A thermodynamic process may be defined as the energetic evolution of a
   thermodynamic system proceeding from an initial state to a final state.
   Typically, each thermodynamic process is distinguished from other
   processes, in energetic character, according to what parameters, as
   temperature, pressure, or volume, etc., are held fixed. Furthermore, it
   is useful to group these processes into pairs, in which each variable
   held constant is one member of a conjugate pair. The six most common
   thermodynamic processes are shown below:
    1. An isobaric process occurs at constant pressure.
    2. An isochoric process, or isometric/isovolumetric process, occurs at
       constant volume.
    3. An isothermal process occurs at a constant temperature.
    4. An isentropic process occurs at a constant entropy.
    5. An isenthalpic process occurs at a constant enthalpy.
    6. An adiabatic process occurs without loss or gain of heat.

The laws of thermodynamics

   In thermodynamics, there are four laws of very general validity, and as
   such they do not depend on the details of the interactions or the
   systems being studied. Hence, they can be applied to systems about
   which one knows nothing other than the balance of energy and matter
   transfer. Examples of this include Einstein's prediction of spontaneous
   emission around the turn of the 20th century and current research into
   the thermodynamics of black holes.

   The four laws are:
     * Zeroth law of thermodynamics, stating that thermodynamic
       equilibrium is an equivalence relation.

                If two thermodynamic systems are separately in thermal
                equilibrium with a third, they are also in thermal
                equilibrium with each other.

     * First law of thermodynamics, about the conservation of energy

                The change in the internal energy of a closed
                thermodynamic system is equal to the sum of the amount of
                heat energy supplied to the system and the work done on
                the system.

     * Second law of thermodynamics, about entropy

                The total entropy of any isolated thermodynamic system
                tends to increase over time, approaching a maximum value.

     * Third law of thermodynamics, about absolute zero temperature

                As a system asymptotically approaches absolute zero of
                temperature all processes virtually cease and the entropy
                of the system asymptotically approaches a minimum value;
                also stated as: "the entropy of a perfectly crystalline
                body at absolute zero temperature is zero."
                See also: Bose–Einstein condensate and negative
                temperature.

Thermodynamic potentials

   As can be derived from the energy balance equation on a thermodynamic
   system there exist energetic quantities called thermodynamic
   potentials, being the quantitative measure of the stored energy in the
   system. The four most well known potentials are:
   Internal energy       U\,
   Helmholtz free energy A=U-TS\,
   Enthalpy              H=U+PV\,
   Gibbs free energy     G=U+PV-TS\,

   Potentials are used to measure energy changes in systems as they evolve
   from an initial state to a final state. The potential used depends on
   the constraints of the system, such as constant temperature or
   pressure. Internal energy is the internal energy of the system,
   enthalpy is the internal energy of the system plus the energy related
   to pressure-volume work, and Helmholtz and Gibbs free energy are the
   energies available in a system to do useful work when the temperature
   and volume or the pressure and temperature are fixed, respectively.

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