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Chemical Thermodynamics

Chemical Thermodynamics. kinetics (little k): told us how fast a RXN would go and indicated a mechanism. Equilibria (big K): told us to what extent a RXN would occur. Themo: the energy involved and if a RXN WILL occur as written. 3-Laws of Thermo.

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Chemical Thermodynamics

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  1. Chemical Thermodynamics

  2. kinetics (little k): told us how fast a RXN would go and indicated a mechanism. Equilibria (big K): told us to what extent a RXN would occur. Themo: the energy involved and if a RXN WILL occur as written.

  3. 3-Laws of Thermo. 1st:Energy is conserved. Enthalpy (H), for a Rxn @ constant pressure the enthalpy change equals the heat transferred between the system and the surroundings. 2nd: A system not @ Equilibrium will move in a natural (spontaneous) direction. Disorder has a positive sign (+) ENTROPY....(S or S)....disorder. S of the universe is increasing (Entropy is not conserved) 3rd: S @ absolute zero of a pure crystalline material = 0. (S = 0 @ 0 K) total order.

  4. spontaneous process: a process that is capable of proceeding in a given direction, as written, without needing to be driven by an outside energy. No rate is implied.

  5. 1st Law of Thermo. (energy is conserved) Review Chapter 5 Esys = Esurroundings  E = q + w work done on (+) or by (-) the sys. heat gained (+) or lost (-) the sys. internal energy - both kinetic and potential of the sys Expansion work: GASES w = -P V = force x distance

  6. Enthalpy: H and H (heat transferred in or out or a system) A State Function

  7. Spontaneous Processes: Have a definite direction in which they will occur. Examples: H2O(s)  H2O(l) @ 1 atm and 40oC H2O(l)  H2O(s) @ 1 atm and -40oC Equilibrium: H2O(s)  H2O(l) @ 1 atm and 0oC Which process is spontaneous?

  8. A process that is spontaneous in one direction is not spontaneous in the opposite direction. • The direction of a spontaneous process can depend on temperature: Ice turning to water is spontaneous at T > 0C, Water turning to ice is spontaneous at T < 0C.

  9. Reversible and Irreversible Processes: A reversible process is one that can go back and forth between states along the same path.

  10. Reversible and Irreversible Processes: • A reversible process is one that can go back and forth between states along the same path. • When 1 mol of water is frozen at 1 atm at 0C to form 1 mol of ice, q = Hfus of heat is removed. • To reverse the process, q = Hfus must be added to the 1 mol of ice at 0C and 1 atm to form 1 mol of water at 0C. • Therefore, converting between 1 mol of ice and 1 mol of water at 0C is a reversible process. • Allowing 1 mol of ice to warm is an irreversible process. To get the reverse process to occur, the water temperature must be lowered to 0C.

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