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Outline: 1/29/07

Outline: 1/29/07. Turn in Seminar reports – to me Today: Student Research Symposium. Outline Free Energy ( D G) & Concentration Lots of practice! D G applications: biochemistry. Summary to date:. D E, D H, D S and D G are defined

brennan-chang
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Outline: 1/29/07

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  1. Outline: 1/29/07 • Turn in Seminar reports – to me • Today: Student Research Symposium • Outline • Free Energy (DG) • & Concentration • Lots of practice! • DG applications: biochemistry

  2. Summary to date: • DE, DH, DS and DG are defined • First law calculations: DE = q + w • DHrxn, DHphasechange problems • DS calculations: T DS = q • DGorxn= DHorxn- TDSorxn problems • Since DHorxn and DSorxn are relatively independent of temperature: • DGTrxn DHorxn- TDSorxn

  3. Worksheet #3: • N2O4(g)<=> 2 NO2(g) • colorless brown • DGo = DG(prdts) - DG(rctnts) • = 2  51 - 98 = +4 kJ • (not spontaneous) • DG77 = DHrxn- (77  DSrxn ) • = 57 - (77  0.176) = +43 kJ • (really not spontaneous!)

  4. DG also depends on concentration…. Worksheet #2: • Demo: N2O4(g)<=> 2 NO2(g) • colorless brown • Clearly a spontaneous reaction at room temperature (298K)…. • Not spontaneous at 77K…. • What’s going on?

  5. Since concentration/dilution alters entropy on a molecular level, standard conditions must also specify concentration: • 1.0 atm for gases • 1.0 M for solns. • Mathematically: • DSrxn = DSorxn- R ln Q • where Q = [C]c[D]d / [A]a[B]b • for the reaction: aA + bB  cC+dD • Q is called the reaction quotient.

  6. Since : • DGTrxn = DHrxn- T DSrxn • Then: • DGTrxn = DHorxn- T(DSorxn - R ln Q) • Or: • DGrxn = DGorxn+ RT lnQ • where Q = reaction quotient • = [prods]/[rcts]

  7. Worksheet #2 (cont’d): • N2O4(g)<=> 2 NO2(g) • colorless brown • What is Q? • = (pNO2 )2/(pN2O4) • Assume pNO2 = pN2O4 = 0.1 atm • Q = 0.1 and • DGrxn = 4 kJ + 0.008314 (298) ln 0.1 • = 4 - 5.7 = - 1.7 kJ • (spontaneous!)

  8. Let’s see how we’re doing… Summary of Thermo: • DE, DH, DS and DG are defined • First law calculations: DE = q + w • DHrxn, DHphasechange problems • DS calculations: T DS = q • DGTrxn DHorxn- TDSorxn problems • DGrxn= DGorxn+ RTlnQ problems

  9. Which of the following has the largest So? • HCl (l) • HCl (s) • HCl (g) • HI (g) • HBr (g)

  10. What is the DG at 100°C for a reaction that has DHo = -271 kJ/mol & DSo = +11.2 J/K? • -272 kJ/mol • -1391 kJ/mol • -275 kJ/mol • -4449 kJ/mol • -282 kJ/mol

  11. Summary of Thermo: • DE, DH, DS and DG are defined • Heat capacity problems: q = n CpDT • First law calculations: DE = q + w • DHrxn, DHphasechange problems • DS calculations: T DS = q • DGTrxn DHorxn- TDSorxn problems • DGrxn= DGorxn+ RTlnQ problems Applications: (what use is thermo?) Nitrogen Fixation, Biochemical energy

  12. What does DG tell us about our planet? ?More common? 

  13. Nitrogen fixation…. Atmospheric nitrogen (NN) is very stable thermodynamically…. Most nitrogen containing compounds have a very positive DG for formation: (e.g. NO, HCN, CH3NH2, CH3CN) Amino acids are our foundation; how do we make them chemically? The process of converting N2 into biologically accessible N is called nitrogen fixation

  14. Nitrogen fixation…. 4 CH3COOH + 2N2+ 2H2O  4 H2NCH2OOH + O2 (glycine) DG = +564 kJ 2 CH3COOH + 2NH3+ O2  2 H2NCH2OOH + 2H2O (glycine) DG = -396 kJ

  15. Nitrogen fixation…. Four basic compounds used to create nitrogenous fertilizer: NH3 HNO3 NH4NO3 (NH2)2CO DGo = negative Ammonia, Nitric acid, Ammonium nitrate, urea

  16. A biochemical use for thermo: • Mammalian metabolism: • ATP + H2O  ADP + H3PO4 DG = -31kJ • 36ADP + 36H3PO4 + 6O2 + C6H12O6 • (energy storage) 36ATP + 6CO2 + 42H2O Adenosine triphosphate (ATP)

  17. Also: Coupled reactions • Mammalian metabolism: necessary reactions that are non-spontaneous are made spontaneous by “coupling” them with ATP • e.g. the production • of glutamine

  18. 1. L-Glutamine is highly correlated to muscle protein synthesis. • 2. Some studies have shown that Glutamine can increase Growth Hormone levels in the body as much as 300%. • 3. L-Glutamine plays a vital role in cell immunity. • 4. L-Glutamine plays a role in nitrogen transport in the body. • example: the production of glutamine

  19. The problem: • glutamic acid + NH3glutamine + H2O • DG = +14 kJ non-spontaneous But… ATP + H2O  ADP + H3PO4 DG = -31kJ So, if these two systems were coupled…

  20. glutamic acid + ATP + NH3 ADP + glutamine + H3PO4 DG = -17 kJ + ATP + H2O  ADP + H3PO4 DG = -31 kJ • glutamic acid + NH3glutamine + H2O DG = +14 kJ This coupling is how many biochemical reaction proceed. It is an example of Hess’ Law. Finish Chapter 14…

  21. Chapters 6 and 14 introduced Thermodynamics: • heat, work, energy, 1st , 2nd laws, state vs. path variables, spontaneity, etc. as related to chemical reactions…. • Chapter 15 introduces: • the rate of reactions (kinetics) • the mechanisms of reactions • These two concepts are closely related on a molecular level!

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