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Unformatted text preview: 1 Clickers on Monday Reversible Processes Free energy (U); enthalpy (H); work; heat 2 What was that lecture about last Tuesday? I have no idea A conversation that was overheard by Chem 1B instructors 3 Other Pathways J atm l w q U Green 1520 15 = ⋅ = + = Δ How about the green path? Why? Because Δ U is a state function – it is pathway independent = all pathways A Æ B 4 Enthalpy V P q V P q w q U P ext P P Δ − = Δ − = + = Δ The work that we have done implies that there is another state function involved here aside from Δ U , the internal energy at constant Pressure (i.e. P = P ext ) 5 Enthalpy V P q V P q w q U P ext P P Δ − = Δ − = + = Δ H PV U V P U q P P Δ = + Δ = Δ + Δ = ) ( PV U H + = Thus, rearranging: Subscript implies constant P Note that q p is in terms of U, P, and V – all are state functions, and so q p is a state function The state function is enthalpy, or H 6 ( ) PV U H Δ + Δ = Δ Enthalpy (defined more generally) ( ) PV T nc V Δ + Δ = ) ( R c T n T nR T nc V V + Δ = Δ + Δ = T nc P Δ = T nc H P Δ = Δ 7 Extracting Work from a System P Volume Figure LS3.1. Two different pathways between A and B. The work for each pathway is represented by the shaded area. Note that if we compress the system along ABC, and expand along the CDA, the net result is that we can get a good yield of work out of the system. A B C P Volume A B C D Work (expansion pathway) Work (compression pathway) P Volume Figure LS3.1. Two different pathways between A and B. The work for each pathway is represented by the shaded area. Note that if we compress the system along ABC, and expand along the CDA, the net result is that we can get a good yield of work out of the system. A B C P Volume A B C D Work (expansion pathway) Work (compression pathway) 8 Extracting Work from a System P Volume Figure LS3.1. Two different pathways between A and B. The work for each pathway is represented by the shaded area. Note that if we compress the system along ABC, and expand along the CDA, the net result is that we can get a good yield of work out of the system. A B C P Volume A B C D Work (expansion pathway) Work (compression pathway) P Volume Figure LS3.1. Two different pathways between A and B. The work for each pathway is represented by the shaded area. Note that if we compress the system along ABC, and expand along the CDA, the net result is that we can get a good yield of work out of the system....
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This note was uploaded on 09/25/2010 for the course CH 104 taught by Professor Bopanna during the Fall '09 term at UMBC.
 Fall '09
 Bopanna
 Enthalpy

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