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I.Thermodynamics

I.AFundamentaldefinitions

•Thermodynamicsisaphenomenologicaldescriptionofequilibriumpropertiesofmacro­

scopicsystems.

⋆Asaphenomenologicaldescription,itisbasedonanumberofempiricalobservations

whicharesummarizedbythelawsofthermodynamics.Acoherentlogicalandmathe­

maticalstructureisthenconstructedonthebasisoftheseobservations,whichleadsto

avarietyofusefulconcepts,andtotestablerelationshipsamongvariousquantities.The

lawsofthermodynamicscanonlybejustifiedbyamorefundamental(microscopic)theory

ofnature.Forexample,statisticalmechanicsattemptstoobtaintheselawsstartingfrom

classicalorquantummechanicalequationsfortheevolutionofcollectionsofparticles.

⋆Asystemunderstudyissaidtobeinequilibriumwhenitspropertiesdonotchange

appreciablywithtimeovertheintervalsofinterest(observationtimes).Thedependence

ontheobservationtimemakestheconceptofequilibriumsubjective.Forexample,window

glassisinequilibriumasasolidovermanydecades,butflowslikeafluidovertimescales

ofmillennia.Attheotherextreme,itisperfectlylegitimatetoconsidertheequilibrium

betweenmatterandradiationintheearlyuniverseduringthefirstminutesofthebigbang.

⋆Themacroscopicsysteminequilibriumischaracterizedbyanumberofthermodynamic

coordinatesorstatefunctions.Somecommonexamplesofsuchcoordinatesarepressure

andvolume(forafluid),surfacetensionandarea(forafilm),tensionandlength(for

awire),electricfieldandpolarization(fora