Lecture_36_PPT

Lecture_36_PPT - Chapter 19-22 Thermodynamics Heat Engines...

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Chapter 19-22 Thermodynamics Heat Engines
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The First Law of Thermodynamics z The only type of energy that changes in a system is internal energy and the energy transfers are by heat and work z E int = Q + W z For infinitesimal changes in a system dE int = dQ + dW
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Isolated Systems z An isolated system is one that does not interact with its surroundings z No energy transfer by heat takes place, Q = 0 z The work done on the system is zero, W = 0 z Q = W = 0, so E int = 0 z The internal energy of an isolated system remains constant
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Isovolumetric Processes z An isovolumetric process is one in which there is no change in the volume z W = 0, E int = Q z If energy is added by heat to a system kept at constant volume, all of the transferred energy remains in the system as an increase in its internal energy z Animation
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Isovolumetric Processes, PV diagram z W = 0, E int = Q z For monoatomic ideal gas, PV = nRT, E int = 3/2 nRT z T i = P i V/nR, T f = P f V/nR, z E int = 3/2 nR ( T f -T i ) z Q = 3/2 nR ( T f -T i ) = 3/2 ( P f -P i ) V
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Isobaric Processes z An isobaric process is one that occurs at a constant pressure z The values of the heat and the work are generally both nonzero z The work done is W = - P ( V f V i ) where P is the constant pressure z Animation
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Isobaric Processes, PV diagram z W = - P ( V f V i ) , E int = Q + W z For monoatomic ideal gas, PV = nRT, E int = 3/2 nRT z T i = PV i /nR, T f = PV f /nR, z Q = E int W =3/2 nR ( T f -T i ) + P ( V f V i ) = 5/2 P ( V f -V i )
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Isothermal Process z An isothermal process is one that occurs at a constant temperature z Since there is no change in temperature, E int = 0 z Therefore, Q = - W z Any energy that enters the system by heat must leave the system by work
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ln ff f ii i VV V V i f nRT dV W P dV dV nRT V Wn R T V =− ⎛⎞ =
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Lecture_36_PPT - Chapter 19-22 Thermodynamics Heat Engines...

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