chapter19

# chapter19 - Thermodynamic systems Isolated systems can...

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Isolated systems can exchange neither energy nor matter with the environment. Closed systems exchange energy but not matter with the environment. Heat Work reservoir Open systems can exchange both matter and energy with the environment. Heat Work reservoir Thermodynamic systems

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Quasi-static processes : near equilibrium Initial state, final state, intermediate state: p, V & T well defined Sufficiently slow processes = any intermediate state can considered as at thermal equilibrium. Thermal equilibrium means that It makes sense to define a temperature. Examples of quasi-static processes: - isothermal: T = constant - isochoric: V = constant - isobaric: P = constant - adiabatic: Q = 0 Quasi-static processes
Work in thermodynamics Expansion: work on piston positive, work on gas negative Compression: work on piston negative, work on gas positive

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Work during a volume change = = = = 2 1 . . V V pdV W pdV Adx p dx F dW
Work in pV diagrams Work done equals area under curve in pV diagram Careful with the signs…

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1 st Law of Thermodynamics W Q U - = Conservation of energy Heat is positive when it enters the system Work is positive when it is done by the system Heat is negative when it leaves the system Work is negative when it is done on the system
1 st Law of Thermodynamics pdV dQ dU - = Conservation of energy Heat is positive when it enters the system Work is positive when it is done by the system Heat is negative when it leaves the system Work is negative when it is done on the system

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) ( 1 2 2 V V p W - = a. isochoric b. isobaric a. isobaric b. isochoric ) ( 1 2 1 V V p W - = = f i V V pdV W isothermal The work done by a system depends on the initial and final states and on the path barb2right it is not a state function. • Amount of heat transferred also depends on the initial, final, and intermediate states barb2right it is not a state function either. (a) (b) (c) State Functions
State Functions 1 2 U U W Q U - = - = The internal energy U is a state function: the energy gain (loss) only depends on the initial and final states, and not on the path.

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