patino_chm2046_chapter17

patino_chm2046_chapter17 - Chapter 17 Free Energy and...

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Chapter 17 Free Energy and Thermodynamics
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Goals Entropy (S, S) and spontaneity Free energy; G, G o G, K, product- or reactant-favored Review : H (Enthalpy) and the 1st Law of Thermodynamics Chemical Equilibria (ch. 14, etc)
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3 First Law of Thermodynamics First Law of Thermodynamics: Energy cannot be created or destroyed the total energy of the universe cannot change it can be transfered from one place to another E universe = 0 = E system + ∆ Ε surroundings system surroundings = everything else (the transfer of energy from one to the other does not change the energy of the universe)
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4 First Law of Thermodynamics For an exothermic reaction, heat from the system goes into the surroundings two ways energy can be “lost” from a system, converted to heat, q used to do work, w Energy conservation requires that the energy change in the system = heat exchanged + work done on the system . E = q + w ( E = internal energy change) E = H – P V ( at const. P , q p = H, enthalpy change) S tate functions (H, P, V). q and w are not. internal energy change ( E ) independent of how done
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5 Enthalpy, H related to (includes) the internal energy H generally kJ/mol stronger bonds = more stable molecules if products more stable than reactants, energy released; exothermic H = negative if reactants more stable than products, energy absorbed; endothermic H = positive The enthalpy is favorable for exothermic reactions and unfavorable for endothermic reactions. Hess’ Law: H ° rxn = Σ ( H f ° prod ) - Σ ( H f ° react )
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6 Thermodynamics and Spontaneity thermodynamics predicts whether a process will proceed (occur) under the given conditions spontaneous process nonspontaneous process does not occur under specific conditions. spontaneity is determined by comparing the free energy (G) of the system before the reaction with the free energy of the system after reaction. if the system after reaction has less free energy than before the reaction, the reaction is thermodynamically favorable. spontaneity fast or slow (rate); this is kinetics
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7 Spontaneous Nonspontaneous ice melts @ 25 o C water freezes @ 25 o C 2Na(s) + 2H 2 O(l) H 2 (g) + 2NaOH(aq) H 2 (g) + 2NaOH(aq) 2Na(s) + 2H 2 O(l) ball rolls downhill ball rolls uphill water freezes @ -10 o C ice melts @ -10 o C
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Diamond → Graphite Graphite is thermodynamically more stable than diamond, so the conversion of diamond into graphite is spontaneous – but it’s kinetically too slow (inert) it will never happen in many, many generations. kinetics
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This note was uploaded on 11/07/2011 for the course CHM 2045 taught by Professor Geiger during the Fall '08 term at University of Central Florida.

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patino_chm2046_chapter17 - Chapter 17 Free Energy and...

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