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Thermodynamics

From Wikipedia, the free encyclopedia

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Annotated color version of the original 1824Carnot heat engineshowing the hot body (boiler),

working body (system, steam), and cold body (water), the letters labeled according to thestopping points inCarnot cycle.

Thermodynamics

Branches[show]

Laws[show]

Systems[show]

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System properties[show]

Material properties[show]

Specific heat capacityc =T

N

Compressibility = 1

V

Thermal expansion =1

V

Equations[show]

Potentials[show]

Internal energy U(S,V)

Enthalpy H(S,p) = U+pVHelmholtz free energyA(T,V) = U TS

Gibbs free energy G(T,p) =H TS

History and culture[show]

Scientists[show]

v d e

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Thermodynamics is the branch ofphysical scienceconcerned withheatand its relation to otherforms of energy andwork. It definesmacroscopicvariables (such astemperature,entropy, andpressure) that describe average properties of material bodies and radiation, and explains how

they are related and by what laws they change with time. Thermodynamics does not describe the

microscopic constituents of matter, and its laws can be derived fromstatistical mechanics.

Thermodynamics can be applied to a wide variety of topics inscienceandengineering, such as

engines,phase transitions,chemical reactions,transport phenomena, and evenblack holes. Theresults of thermodynamics are essential for other fields ofphysicsand forchemistry,chemical

engineering,aerospace engineering,mechanical engineering,cell biology,biomedical

engineering,materials science, and are useful for other fields such aseconomics.[1][2]

Much of the empirical content of thermodynamics is contained in its four laws. The first law

specifies that energy can be exchanged between physical systems asheatandthermodynamic

work.[3]

The second law concerns a quantity calledentropy, that expresses limitations, arisingfrom what is known as irreversibility, on the amount of thermodynamic work that can be

delivered to an external system by a thermodynamic process.

[4]

Historically, thermodynamics developed out of a desire to increase theefficiencyof earlysteam

engines, particularly through the work of French physicistNicolas Lonard Sadi Carnot(1824)

who believed that the efficiency of heat engines was the key that could help France win theNapoleonic Wars.[5]Scottish physicistLord Kelvinwas the first to formulate a concise definition

of thermodynamics in 1854:[6]

Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts

of bodies, and the relation of heat to electrical agency.

Initially, the thermodynamics of heat engines concerned mainly the thermal properties of their'working materials', such as steam. This concern was then linked to the study of energy transfers

in chemical processes, for example to the investigation, published in 1840, of the heats ofchemical reactions[7]byGermain Hess, which was not originally explicitly concerned with the

relation between energy exchanges by heat and work.Chemical thermodynamicsstudies the role

ofentropyinchemical reactions.[8][9][10][11][12][13][14][15][16]

Also,statistical thermodynamics, orstatistical mechanics, gave explanations of macroscopic thermodynamics bystatistical

predictions of the collective motion of particles based on the mechanics of their microscopic

behavior.

Contents

[hide]

1 Introduction 2 History

o 2.1 Etymology 3 Branches of description

o 3.1 Classical thermodynamics

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o 3.2 Statistical thermodynamicso 3.3 Chemical thermodynamics

4 Thermodynamic equilibrium 5 Laws of thermodynamics 6 System models 7 States and processes

o 7.1 Thermodynamic state variableso 7.2 Equation of stateo 7.3 Thermodynamic processes

7.3.1 Dependent and independent variables for a process 7.3.2 Changes of state of a system 7.3.3 Cyclic processes 7.3.4 Commonly considered thermodynamic processes

8 Instrumentation 9 Conjugate variables 10 Potentials 11 Axiomatics 12 Scope of thermodynamics 13 Applied fields 14 See also

o 14.1 Lists and timelineso 14.2 Wikibooks

15 References 16 Bibliography 17 Further reading 18 External links

[edit] Introduction

The plain term 'thermodynamics' refers to macroscopic description of bodies and processes.[17]

"Any reference to atomic constitution is foreign to ... thermodynamics".[18]The qualified term

'statistical thermodynamics' refers to descriptions of bodies and processes in terms of the atomic

constitution of matter.

Thermodynamics is built on the study of energy transfers that can be strictly resolved into two

distinct components,heatandwork, specified by macroscopic variables.[19][20]

Thermodynamic equilibriumis one of the most important concepts for thermodynamics.

Thermodynamics is well understood and validated for systems in thermodynamic equilibrium,but as the systems and processes of interest are taken further and further from thermodynamic

equilibrium, their thermodynamical study becomes more and more difficult. Systems in

thermodynamic equilibrium have very well experimentally reproducible behaviour, and as

interest moves further towards non-equilibrium systems, experimental reproducibility becomesmore difficult. The present article takes a gradual approach to the subject, starting with a focus

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on cyclic processes and thermodynamic equilibrium, and then gradually beginning to further

consider non-equilibrium systems.

For thermodynamics and statistical thermodynamics to apply to a process in a body, it is

necessary that the atomic mechanisms of the process fall into just two classes: those so rapid

that, in the time frame of the process of interest, the atomic states effectively visit all of theiraccessible range, and those so slow that their effects can be neglected in the time frame of the

process of interest.[21]

The rapid atomic mechanisms mediate the macroscopic changes that are ofinterest for thermodynamics and statistical thermodynamics, because they quickly bring the

system near enough to thermodynamic equilibrium. "When intermediate rates are present,

thermodynamics and statistical mechanics cannot be applied."[21]

The intermediate rate atomicprocesses do not bring the system near enough to thermodynamic equilibrium in the time frame

of the macroscopic process of interest. This separation of time scales of atomic processes is a

theme that recurs throughout the subject.

Basic for thermodynamics are the concepts ofsystemandsurroundings.[12][22]

There are two fundamental kinds of entity in thermodynamics, states of a system, and processes

of a system. This allows two fundamental approaches to thermodynamic reasoning, that in terms

of states of a system, and that in terms of cyclic processes of a system.

A thermodynamic system can be defined in terms of its states. In this way, a thermodynamicsystem is amacroscopicphysical object, explicitly specified in terms of macroscopic physicaland chemical variables which describe its macroscopic properties. The macroscopic state

variables of thermodynamics have been recognized in the course of empirical work in physics

and chemistry.[13]

A thermodynamic system can also be defined in terms of the processes which it can undergo. Ofparticular interest are cyclic processes. This was the way of the founders of thermodynamics in

the first three quarters of the nineteenth century.

The surroundings of a thermodynamic system are other thermodynamic systems that can interactwith it. An example of a thermodynamic surrounding is a heat bath, which is considered to be

held at a prescribed temperature, regardless of the interactions it might have with the system.

The macroscopic variables of a thermodynamic system can under some conditions be related to

one another throughequations of state. They express the constitutive peculiarities of the material

of the system. Classical thermodynamics is characterized by its study of materials that have

equations of state that express relations between mechanical variables and temperature that arereached much more rapidly than any changes in the surroundings. A classical material can

usually be described by a function that makes pressure dependent on volume and temperature,

the resulting pressure being established much more rapidly than any imposed change of volume

or temperature.[23]

Thermodynamic facts can often be explained by viewing macroscopic objects as assemblies ofvery many microscopic oratomicobjects that obeyHamiltonian dynamics.[12][24][25]The

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microscopic or atomic objects exist in species, the objects of each species being all alike.

Because of this likeness, statistical methods can be used to account for the macroscopicproperties of the thermodynamic system in terms of the properties of the microscopic species.

Such explanation is calledstatistical thermodynamics; also often it is also referred to by the term

'statistical mechanics', though this term can have a wider meaning, referring to 'microscopic

objects', such as economic quantities, that do not obey Hamiltonian dynamics.

[24]

Thethermodynamicistsrepresentative of the original eight founding schools of thermodynamics.The schools with the most-lasting effect in founding the modern versions of thermodynamics are

the Berlin school, particularly as established inRudolf Clausiuss 1865 textbookThe Mechanical

Theory of Heat, the Vienna school, with thestatistical mechanicsofLudwig Boltzmann, and the

Gibbsian school at Yale University, American engineerWillard Gibbs' 1876On the Equilibrium

of Heterogeneous Substanceslaunchingchemical thermodynamics.[26]

[edit] History

Thehistory of thermodynamicsas a scientific discipline generally begins withOtto von Guerickewho, in 1650, built and designed the world's firstvacuum pumpand demonstrated avacuum

using hisMagdeburg hemispheres. Guericke was driven to make a vacuum in order to disproveAristotle's long-held supposition that 'nature abhors a vacuum'. Shortly after Guericke, theEnglish physicist and chemistRobert Boylehad learned of Guericke's designs and, in 1656, in

coordination with English scientistRobert Hooke, built an air pump.[27]Using this pump, Boyle

and Hooke noticed a correlation betweenpressure,temperature, andvolume. In time,Boyle's

Lawwas formulated, which states that pressure and volume areinversely proportional. Then, in1679, based on these concepts, an associate of Boyle's namedDenis Papinbuilt asteam digester,

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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

a cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697,based on Papin's designs, engineerThomas Saverybuilt the first engine, followed byThomas

Newcomenin 1712. Although these early engines were crude and inefficient, they attracted theattention of the leading scientists of the time.

The fundamental concepts ofheat capacityandlatent heat, which were necessary for thedevelopment of thermodynamics, were developed by ProfessorJoseph Blackat the University of

Glasgow, whereJames Wattwas employed as an instrument maker. Watt consulted with Black

in order to conduct experiments on his steam engine, but it was Watt who conceived the idea of

theexternal condenserwhich resulted in a large increase insteam engineefficiency.[28]

Drawingon all the previous work ledSadi Carnot, the "father of thermodynamics", to publishReflections

on the Motive Power of Fire(1824), a discourse on heat, power, energy and engine efficiency.The paper outlined the basic energetic relations between theCarnot engine, theCarnot cycle, andmotive power. It marked the start of thermodynamics as a modern science.[15]

The first thermodynamic textbook was written in 1859 byWilliam Rankine, originally trained asa physicist and a civil and mechanical engineering professor at theUniversity of Glasgow.[29]

The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily

out of the works ofWilliam Rankine,Rudolf Clausius, andWilliam Thomson(Lord Kelvin).

The foundations of statistical thermodynamics were set out by physicists such asJames Clerk

Maxwell,Ludwig Boltzmann,Max Planck,Rudolf ClausiusandJ. Willard Gibbs.

During the years 187376 the American mathematical physicistJosiah Willard Gibbspublished

a series of three papers, the most famous beingOn the Equilibrium of Heterogeneous

Substances,[8]in which he showed howthermodynamic processes, includingchemical reactions,

could be graphically analyzed, by studying theenergy,entropy,volume,temperatureand

pressureof thethermodynamic systemin such a manner, one can determine if a process wouldoccur spontaneously.[30]AlsoPierre Duhemin the 19th century wrote about chemical

thermodynamics.[9]

During the early 20th century, chemists such asGilbert N. Lewis,Merle

Randall,[10]

andE. A. Guggenheim[11][12]

applied the mathematical methods of Gibbs to theanalysis of chemical processes.

[edit] Etymology

The etymology ofthermodynamics has an intricate history.[31]It was first spelled in a hyphenated

form as an adjective (thermo-dynamic) and from 1854 to 1868 as the noun thermo-dynamics to

represent the science of generalized heat engines.[31]

The components of the word thermodynamics are derived from theGreekwordstherme,

meaning heat, anddynamis, meaning power.[32][33][34]