Lecture25 - Chem 162, Lect 25, Spring 2011 Three Laws of...

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Chem 162, Lect 25, Spring 2011 Three Laws of Thermo: We divide the Universe into the System and the Surroundings (everything but the System). The System undergoes a change from some initial state to some final state (a physical or chemical change). Universe = System + Surroundings First law of thermodynamics : Conservation of energy; “energy can be neither created nor destroyed” – the total energy of the Universe is constant. Energy book-keeping…. .”You can’t win” U Univ = U Sys + U Surr = constant U Univ = U Sys + U Surr = 0 U Sys = q + w q = heat added to system; w = work done on system Change ( ) always means “final state minus initial state”. Typical changes examined previously include: H = U + PV H = H final – H initial := change in enthalpy H = (U + PV) = U + (PV) = U + (P final V final -P initial V initial ) = U + P initial (V final -V initial ) = U + P V at constant P (P final =P initial ) 1
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S = S final – S initial := change in entropy (T S will be an energy quantity) G = G final – G initial := change in (Gibbs) free energy ( G = ∆Η –T S at constant T) H, S, and G are all state functions Second Law of Thermodynamics : In any spontaneous process there is always an increase in the entropy of the Universe. The entropy of the Universe is always increasing (“You can’t even stay even”) S Univ = S Sys + S Surr > 0 for spontaneous process < 0 for non-spontaneous process = 0 equilibrium(!!) The driving force for a spontaneous process is an increase in the entropy of the Universe. A non-spontaneous process decreases the entropy of the Universe. A process which does not change the entropy of the Universe is at equilibrium!
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Lecture25 - Chem 162, Lect 25, Spring 2011 Three Laws of...

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