9_Thermodynamics_1

9_Thermodynamics_1 - Chapter 19 Chemical Thermodynamics...

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Chapter 19 Chemical Thermodynamics 1 Thermodynamics Entropy and Spontaneity
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Kine8cs vs. Thermodynamics Rates of chemical reac8ons are controlled by ac8va8on energy – lower Ea, faster rate. Collision frequency; collisions, rate Equilibrium is reached when rate forward = rate reverse, also depends on energy (temp). Thermodynamics explores connec8on between energy and the EXTENT of a reac8on but tells you nothing about reac8on rates. 2 Thermodynamics Entropy and Spontaneity
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3 Thermodynamics Entropy and Spontaneity
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State functions are written as uppercase letters (E, H, P, V, T, S…) Changes in state functions are path-independent: reactants products E 1 2 A state function: is a quantity that does not depend on the process by which the system was prepared q and w are not state functions but E (= q + w) is a state function 4 Thermodynamics Entropy and Spontaneity Example: Your altitude (height above sea level) does not depend on the route you took to class this morning.
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THERMOCHEMISTRY 1 st Law of Thermodynamics: Δ E universe = 0 Δ E universe = Δ E system + Δ E surroundings Δ E system = Δ E surroundings Heat and work: E system = q + w and for PV work at const. pressure, E system = q – P V 5 Thermodynamics Entropy and Spontaneity
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H = heat transferred at const. P If (+): If ( ): Classify as endo- or exo- thermic : Ice melting Water boiling Wood burning 6 Thermodynamics Entropy and Spontaneity H is a state function – changes are path-independent H = E + PV (sums and products of state functions are also state functions)
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H o f : H for making 1 mole of a compound from its component elements in their standard states Standard state is the most stable form (pure solid, pure liquid, or gas at P = 1 atm and 298K) For solutes in solution, standard state is usually 1 M . Appendix C provides values of H o f H o rxn = Σ H o f (products) Σ H o f (reactants) 7 Thermodynamics Entropy and Spontaneity
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Spontaneous processes: Processes that are spontaneous in one direc8on are nonspontaneous in the reverse direc8on. ± Thermodynamics Entropy and Spontaneity
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This note was uploaded on 01/18/2012 for the course CHEM 112 taught by Professor Vandersluys,lorschmid,kylem during the Summer '07 term at Penn State.

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9_Thermodynamics_1 - Chapter 19 Chemical Thermodynamics...

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