Thermodynamics

1. Thermodynamics Introduction

3. Thermodynamics Transport, transformation and effect(s) of an organic compound depend on which environmental compartment it settles in. Examples: Compounds can be transported long distances in air or water, but if they remain sorbed to organic matter, their movement is limited. (Like a �Broken down Mac Truck�) CCl2F2 may undergo reductive dehalogenation in anaerobic aqueous environments, but due to its very high vapor pressure, it stays in the atmosphere, which is oxidative. Thus CCl2F2 is very persistent and eventually reaches the stratosphere, where it causes ozone depletion.

4. Thermodynamics Quantifies a compound�s affinity for the environmental compartments which are available to it. Also implies the amount of energy necessary to move a chemical into a different compartment Can predict the direction of phase transfer Example: Are PBDEs absorbing into or volatilizing out of the water of the Hudson River Estuary? Does not tell us anything about kinetics of phase transfer

5. Equilibrium is related to kinetics

6. In addition, Kinetic expressions for things like air-water exchange include the thermodynamic constant (Henry�s law constant). Sometimes equilibrium can be related to kinetics via Linear Free Energy Relationships

7. Chemical potential (m) Energy status of molecules in a system (e.g. Benzene in water) Internal energies Chemical Bonds, vibrations, flexations, rotations. External Energies Whole molecule transitions, orientations Interactions of molecule with surroundings Energy status is a function of: Temperature Pressure Chemical composition �Average energy per molecule�

8. Chemical potential = free energy added to system with each added increment of i

9. If two populations of chem (for example, the chemical coexists in two separate phases): each will have its own value of m1 and m2

10. No way to directly measure chemical potential. Can only determine differences in m, based on the tendencies of a chemical to move from one situation to another. Need a reference point, like sea level or absolute zero. often: select pure liquid chem. as reference

11. Fugacity = urge to flee Fugacity is how happy the chemical is in its environment Fugacity is like temperature. At equilibrium, everything has the same fugacity (temperature) even though they may contain different concentrations (amounts) of the chemical (heat).

12. Fugacity vs. Temperature

13. Reference states For gases, ideal behavior is assumed, so a compound�s fugacity is equal to its partial pressure:

14. For pure solid (s) or liquid (L), the fugacity is:

15. In a mixture (i.e. aqueous solution):

16. Activity coefficient and chemical potential �

17. Phase transfer processes(or: where the rubber hits the road)

18. After some rearranging you get:

19. contributions from enthalpy and entropy terms Water-building of H-bonded cage around each solute molecule accounts for large positive (unfavorable) entropy change Note how most things have a similar entropy of vaporization, except ethanol, which undergoes extensive H bonding in the liquid phase.Water-building of H-bonded cage around each solute molecule accounts for large positive (unfavorable) entropy change Note how most things have a similar entropy of vaporization, except ethanol, which undergoes extensive H bonding in the liquid phase.

20. Temperature dependence of K