Thermodynamics: Energy Changes and Entropy, Slides of Thermodynamics

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Entropy, Equilibrium, Irreversibility:

The 2

nd

Law of Thermodynamics and

its numerous consequences

Henning Struchtrup Victoria, BC, Canada AICES Short Course, RWTH Aachen, Sept. 2, 2015

Approach to Thermodynamics

(and every other science)

• Observe
• Generalize observaDons
• Formulate laws in words/ as equaDons
• Evaluate laws, make predicDons
• Understand laws (if possible)

Thermodynamics at Work

Hot coffee in cold kitchen: EquilibraDon of temperature

Thermodynamics at Work

Coffee and milk

Thermodynamics at Work

Let’s sDr the coffee (and remove spoon)

Thermodynamics at Work

Let’s sDr the coffee (and remove spoon): coffee comes to rest

The 2

nd

Law of Thermodynamics

describes the approach to equilibrium of any system note: conservaDon laws alone do not suffice! example: Energy conservaDon ( st law) allows coffee to cool and spin faster, but this is against the 2 nd law for proper formulaDon of 2 nd law, we need some background and more language

fast process: system is in inhomogeneous states; aXer manipulaDon stops, process conDnues unDl equilibrium state  Approach to equilibrium is an uncontrolled process irreversible: backward movie never observed, ie, impossible

Processes and Equilibrium

Quasi-­‐equilibrium process: slow manipulaDon, so that system is in equilibrium states at any Dme; when manipulaDon stops, no further changes occur. System can be described by few parameters (volume, temperature, pressure), typically homogeneous states. reversible: can’t disDnguish whether movie is forward or backward all real life processes are irreversible !!

The Closed System

no exchange of mass with the surroundings only means of manipulaDon:

• piston work
• propeller work
• heat exchange

th

law: Temperature

two bodies of temperatures assume common temperature T a while aXer brought into contact defines temperature as a measurable property note: this is an equilibraDon process

kineDc energy potenDal energy internal energy

Energy and other properLes

u ( , T )  caloric equaDon of state: internal (or, thermal) energy p ( , T )  thermal equaDon of state: pressure  – mass density, V – velocity, g – gravity, V – volume

Simple EquaLon of States

 specific heat at constant volume (depends on material) ideal gas (const. spec. heat): , incompressible liquid/solid: ,  specific volume (depends on material)

transfer of energy due to differences in temperature

Heat Transfer

Heat will always go from hot to cold by

itself, but not vice versa!!

heat exchanged during process 1-­‐2: heaDng rate:

The 2

nd

Law of Thermodynamics

isolated system approaches equilibrium define property entropy S with non-­‐negaDve producDon state of the system changes (ie, process conDnues) unDl final stable state, where S is maximum and  generalize to non-­‐isolated systems  find property relaDon for S