c103-sp10-0505b

c103-sp10-0505b - Chemistry 103 Spring 2010 To d a y 1....

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Chemistry 103 Spring 2010 Today 1. Second law of thermodynamics. 2. Free energy combines entropy and enthalpy. Announcements 1. Ch. 14-17 OWL homework is active. 2. Next midterm exam on May 17 or 19. 3. CSULA closure on May 21 (furlough). 4. CSULA closure on May 31 (holiday). 5. Bring textbook and calculator to each lecture.
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Chemistry 103 Spring 2010 2 Three laws of thermodynamics First law of thermodynamics : law of conservation of energy; energy can neither be created or destroyed; total energy of universe is constant; energy is conserved. (Chapter 6) Δ E(gained by system) + Δ E(lost by surroundings) = 0 Δ E(gained by surroundings) + Δ E(lost by system) = 0 Δ E universe = 0 Δ E system + Δ E surroundings = 0 Δ E system = - Δ E surroundings Third law of thermodynamics : a perfect crystal of any substance at 0 K has zero entropy. S = 0 at 0 K
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Chemistry 103 Spring 2010 3 Second law of thermodynamics : the total entropy of the universe is increasing. The energy of the universe constantly becomes more dispersed and spread out over time. Δ S universe > 0 Δ S system + Δ S surroundings > 0 We could decrease the entropy of a system, e.g., organize a messy living room. ( Δ S system < 0) But it could only happen if the entropy of the surroundings increased ( Δ S surroundings > 0) and increased by more than the magnitude of the decrease in the system: Δ S system + Δ S surroundings > 0 … Δ S system < 0, Δ S surroundings > - Δ S system so - Δ S system > 0 In other words, the decrease only happens by dispersing more energy in the surroundings (we spend energy to clean up the room), so the total entropy of the universe increases.
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4 Example : For the following process at 25 ºC, what is the entropy change of the system? Of the surroundings? Of the universe? Could this be a useful way to produce methanol for fuel? CO(g) + 2H
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c103-sp10-0505b - Chemistry 103 Spring 2010 To d a y 1....

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