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First Law of Thermodynamics Introduction First Law of Thermodynamics Calculation of Work PVT diagrams Thermodynamic processes Simple Examples The “everything” problem More examples

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Perspective

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First Law of Thermodynamics +Q-W +W-Q UU

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Work by expanding gas

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PVT diagrams – Viewing P,V,T

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PVT diagrams – Viewing Work

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PVT diagrams – Filling in the Heat

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Thermodynamic Processes I

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Thermodynamic Processes II

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4 thermodynamic paths A= isovolumetric – Volume constant. – Pressure drop. – Lower temperature and U. – No work. D= isobaric – Volume increase. – No Pressure change. – Higher temperature and U. – Work out. C= isothermal – Volume increase. – Pressure decrease. – No temperature U and change. – Work out. B = adiabatic – Volume increase. – Pressure decrease. – Temperature and U decrease. – Work out.

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Example 15-5 (1)

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Example 15-5 (2)

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Example 15-6

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The “everything” problem One mole of an ideal gas undergoes the series of processes shown in the figure. (a) Calculate the temperature at points A, B, C and D. (b) For each process A B, B C, C D, and D A, calculate the work done by the process. (c) Calculate the heat exchanged with the gas during each of the four processes. (d) What is the net work done during the entire process? (e) What is the net heat added during the entire process? (f) What is the thermodynamic efficiency?

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“Everything” problem – calculate temperatures & Internal Energies

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“Everything” problem – calculate works

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“Everything” problem – fill in 1 st law table ΔUΔUWorkQ a -> b+6000 J+4000 J b -> c-4500 J0 J c -> d-3000 J-2000 J d -> a+1500 J0 J

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“Everything” problem – fill in Q’s ΔUΔUWorkQ a -> b+6000 J+4000 J10000 J b -> c-4500 J0 J-4500 J c -> d-3000 J-2000 J-5000 J d -> a+1500 J0 J1500 J entire cycle0 J2000 J Net work during entire cycle 2000J Net heat absorbed/expelled during cycle 2000 J Change in internal energy during cycle 0 J Net Heat in equals net work out. Change in internal energy zero

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“Everything” problem – getting efficiency ΔUΔUWorkQ a -> b+6000 J+4000 J10000 J b -> c-4500 J0 J-4500 J c -> d-3000 J-2000 J-5000 J d -> a+1500 J0 J1500 J entire cycle0 J2000 J

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“Everything” problem – Shortcut for ΔUs ΔUΔUWorkQ a -> b+6000 J+4000 J b -> c-4500 J0 J c -> d-3000 J-2000 J d -> a+1500 J0 J

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Animations Add heat, increase temperature/pressure at constant volume. Add heat, increase temperature/volume at constant pressure. Add and remove heat, expand and compress gas. (Otto cycle)

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Problem 10 a)Do A and C agree on temperature? No. Point C should be 10.7 L b) What is work done abc? c) What is change of internal energy abc? d) What is heat flow abc?

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Problem 10 (cont)

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Problem 11 a)Find temperature at 1 and 2 b)Find 1-step work from 1 to 2 c)Find 1-step internal energy change 1 to 2 d)Find 2-step internal energy change 1 to 2

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Problem 12

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Questions?

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