Spontaneity: Effect of Configurations on Reactions

1. “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #20 Spontaneity Effect of number of Possible configurations (randomness) on reactions

2. A + BC + heat A + B + heatC What we’ve Learned So Far Energy Ea Ea endothermic exothermic Does not tell us if spontaneous or not

3. A messy room is more probable than an organized one. Can think of this as stored energy. spontaneous? or probable?

4. OJO Spontaneous Reactions: heat or randomness -heat +randomness reactants products -heat -H + randomness +S

5. Randomness = more possibilities = entropy (S) What is the most probable configuration for n tossed quarters? 2 coins 1 1 coin=2 sides 2 1 Most probable configuration is least organized 2 configurations =21 4 configurations =22

6. What will the pattern be for three coins? 1 3 3 1 3 coins 8 configurations = 23 4 coins ? configurations = 2? • Most probable configuration is least organized • Number of possible configuration increases exponentially • No. configurations contains information about compound (sides)

7. Probability of finding An electron – everywhere! Very random How does this affect the trends in entropy of various elements? 1s electron

8. 2p electron probability Is more confined – less Random, less entropy

9. Probability of Finding an electron For a d orbital – More spatially constrained, Less entropy

10. Entropy and Atomic Mass • Entropy contraction across row – related to organization of electrons • Entropy increase down group – related to volume occupied Half filled d

11. Entropy and Group What do you observe? Same observations!

12. “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #20 Spontaneity Reaction Entropy

13. The change in entropy in a reaction is the difference between the summed entropy of the products minus the summed entropy of the reactants scaled by the number of moles

14. Example Calculation 1: Calculate the change in reaction entropy that occurs for each of the following two phase changes given the data below: So (J/mol-K) Cs(s) 85.15 Cs(l) 92.07 Cs(g) 175.6

15. Example Calculation 1: Calculate the change in reaction entropy that occurs for each of the following two phase changes given the data below: So (J/mol-K) Cs(s) 85.15 Cs(l) 92.07 Cs(g) 175.6

16. Spontaneous Reactions: heat or randomness -heat Reactions Increase the Spontaneity By an increase In randomness +randomness reactants products -heat -H + randomness +S

17. So (J/mol-K) H2O(l) 69.91 H2O(g) 188.83 Hg(l) 77.40 Hg(g) 174.89 Cs(s) 85.15 Cs(l) 92.07 Cs(g) 175.6 “Medicine is the Art of Observation” (Al B. Benson) What do you observe? • Large change liquid to gas • S depends on Temp!!!

18. Some typical Standard S values “Medicine is the Art of Observation” Let’s rearrange to make this a little easier

19. Pure Liquid Solids Gas Aqueous Do we notice anything? Prediction reactions producing more Gas phase species will increase in entropy 1. More atoms = more S • Pure liquids higher S than s • Aqueous species can have neg S! Why? 4. Gas highest S

20. Possible configurations? solid < glass, plastic, liquid < gas Ssolid < Ssolid, plastic,liquid < Sgas S Note: this Refers to a single Molecule or element Water ice, liquid, gas Absolute Zero, no motion T (K)

21. A closely related idea to change in entropy In phase changes is the change in entropy in Going from individual ligands to chelates From Module 18 we considered the electrostatic attraction between the electron pairs on ligand functional groups and the positive nucleus of a metal ion. Module 18 review

22. z x y Module 18 review

23. We observed that multidentate ligands had very high Kf values Which are polydentate? What do you observe? Why so large? Module 18 review

24. Example 2: Predict the entropy change in the following reaction by considering volume occupied and number of possible configurations between the reactants and products Note that the electrostatic attraction which shows up in the enthalpy is similar for both compounds

25. Example 2: Predict the entropy change in the following reaction by considering volume occupied and number of possible configurations between the reactants and products 5 3 J. Chem. Ed. 61,12, 1984, Entropy Effects in Chelation Reactions, Chung-Sun Chung

26. Example Calculation 3: Calculate the reaction entropy changes for the reaction shown below given: So (J/mol-K) S rhombic 32 S orthoclinic 33 Cu(s) 85.15 CuS(s) 92.07 Cu2S(s) 175.6 First let’s think about this a bit • Internal Entropy • a.Why should CuS have more entropy than Cu? • b. Why should Cu2S have much more entropy than CuS?

27. Which one might have More configurations? http://images.google.com/imgres?imgurl=http://www.unisa.edu.au/synchrotron/res/projects/chalcociteCu2S.jpg&imgrefurl=http://www.unisa.edu.au/synchrotron/res/projects/default.asp&h=242&w=180&sz=20&hl=en&start=7&um=1&tbnid=UYBN7p1lBciHwM:&tbnh=110&tbnw=82&prev=/images%3Fq%3DCu2S%2B%26svnum%3D10%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26channel%3Ds%26rls%3Dorg.mozilla:en-US:official%26sa%3DG http://www.haraldthielenredlich.onlinehome.de/kkch/cu1+cu2s.jpg

28. A single, individual, H atom can occupy 4 Different locations – thus the compound will be More random than one with three locations for The hydrogen So (J/mol-K) CH4 186. C2H4 219.4 This reflects internal entropy which often scales with # of Atoms in the molecule.

29. Example Calculation 3: Calculate the reaction entropy changes for the reaction shown below given: So (J/mol-K) S rhombic 32 S orthoclinic 33 Cu(s) 85.15 CuS(s) 92.07 Cu2S(s) 175.6 2 1 First let’s think about this a bit • Spatial Volume of rx entropy • Which will be more imp in rx entropy? Internal entropy or spatial volume entropy? We take two separate chemical units and make Them into 1 chemical unit – implies decrease in entropy

30. Example Calculation 3: Calculate the reaction entropy changes for the reaction shown below given: So (J/mol-K) S rhombic 32 S orthoclinic 33 Cu(s) 85.15 CuS(s) 92.07 Cu2S(s) 175.6

31. Example Calculation 3: Calculate the reaction entropy changes for the reaction shown below given: So (J/mol-K) S rhombic 32 S orthoclinic 33 Cu(s) 85.15 CuS(s) 92.07 Cu2S(s) 175.6 1 2

32. Example Calculation 4: Calculate the change in entropy for the allotropic forms of elemental S So (J/mol-K) S rhombic 32 S orthoclinic 33 Cu(s) 85.15 CuS(s) 92.07 Cu2S(s) 175.6 Gr: allos = others

34. “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #20 Spontaneity Entropy of the surroundings

35. Spontaneous Process: Universal entropy increases (The universe is winding down.)

36. Example 1: Ssurroundings Change in Ssurroundings? Change in Sreaction? heat will increase kinetic energy of gases = Ssurround >0 More organized (fewer molecules) implies less entropy, less random Sreaction<0

37. Example 2: Ssurroundings From surroundings, withdraw heat, Less kinetic energy, less motion, less entropy + heat Although this process requires heat, it is spontaneous, driven by entropy of chemical reaction Reaction less random rx more random

38. The two reactions (the system) Interact with the surroundings by exchange of heat Heat of reaction must be related to entropy of surroundings

39. “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #20 Spontaneity Randomness of the “surroundings” affected By enthalpy

40. related to enthalpy or heat of reaction proportional Where will impact on Ssurroundings be greatest? a. 1 J at 600oC b. 1 J at 25oC

41. Predict entropy change is largest at low temperatures sign change accounts for the fact that entropy increases with exothermic reactions

42. Context Slide for a calculation on entropy of the surroundings Historically Ag was mined as Ag2S found in the presence of PbS, galena. Part of the process of releasing the silver required oxidizing the galena. The lead oxide recovered was used in glass making. The fumes often killed animals near by and have left a permanent record in the artic ice. Large regions near silver mines were deforested. One reason that this process was discovered so early in history was The low temperature at which it could be carried out. Lead in Artic Ice Who has the “honor” of most contaminating The artic ice? Medicine is the art of observation Yorkshire, near old lead mines

43. Calculating Ssurrounding Example 1 Compare the change in entropy of the surroundings for this reaction at room temperature and at the temperature of a campfire (~600 oC). Know: Don’t know red herrings? reaction none entropy

44. Substance Hf0 (kJ/mole) O2(gas) 0 PbS -100 PbO -219 SO2(gas) -297

45. Calculating Ssurrounding Example 1 Compare the change in entropy of the surroundings for this reaction at room temperature and at the temperature of a campfire (~600 oC). Our prediction was right! Larger at low T

46. “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #20 Spontaneity Total Entropy change With reaction enthalpy

48. Reaction Entropy Example Calculation 3 Compare the total entropy change for the following reaction at 25oC and 600oC Substance S0 (J/K-mole) O2(gas) 205 PbS(solid) 91 PbO(solid) 66.5 SO2(gas) 248

49. Reaction Entropy Example Calculation 3 Compare the total entropy change for the following reaction at 25oC and 600oC

50. Less spontaneous Spontaneous