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

Summary to date:   E,  H,  S and  G are defined  First law calculations:  E = q + w   H rxn,  phase change problems   S calculations: T  S = q   G o rxn =  H o rxn  T  S o rxn problems  Since  H o rxn and  S o rxn are relatively independent of temperature:   G T rxn   H o rxn  T  S o rxn

Worksheet #3:  N 2 O 4(g)  2 NO 2(g) colorless brown   G o =  G(prdts)  G(rctnts)  = 2  51  98 = +4 kJ (not spontaneous)   G 77 =  rxn  S rxn )  = 57  77  0.176) = +43 kJ (really not spontaneous!)

Worksheet #2:  Demo: N 2 O 4(g)  2 NO 2(g) colorless brown Clearly a spontaneous reaction at room temperature (298K)…. Not spontaneous at 77K…. What’s going on?   G also depends on concentration….

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:   S rxn =  S o rxn  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.

   G rxn =  G o rxn  RT lnQ where Q = reaction quotient = [prods]/[rcts] Since :   G T rxn =  H rxn  T  S rxn Then:   G T rxn =  H o rxn  T(  S o rxn  R ln Q) Or:

Worksheet #2 (cont’d):  N 2 O 4(g)  2 NO 2(g) colorless brown What is Q? = (p NO2 ) 2 /(p N2O4 ) Q = 0.1 and   G rxn =  kJ  (298) ln 0.1  = 4  7  1.7 kJ (spontaneous!) Assume p NO2 = p N2O4 = 0.1 atm

Summary of Thermo:   E,  H,  S and  G are defined  First law calculations:  E = q + w   H rxn,  phase change problems   S calculations: T  S = q   G T rxn   H o rxn  T  S o rxn problems   G rxn =  G o rxn  RTlnQ problems Let’s see how we’re doing…

Which of the following has the largest S o ? HCl (l) HCl (s) HCl (g) HI (g) HBr (g)

What is the  G at 100 ° C for a reaction that has  H o =  271 kJ/mol &  S o = J/K?    272 kJ/mol    1391 kJ/mol    275 kJ/mol    4449 kJ/mol    282 kJ/mol

Summary of Thermo:   E,  H,  S and  G are defined  Heat capacity problems: q = n C p  T  First law calculations:  E = q + w   H rxn,  phase change problems   S calculations: T  S = q   G T rxn   H o rxn  T  S o rxn problems   G rxn =  G o rxn  RTlnQ problems Applications: (what use is thermo?) Nitrogen Fixation, Biochemical energy

What does  G tell us about our planet?  ?More common? 

Nitrogen fixation…. Atmospheric nitrogen (N  N) is very stable thermodynamically…. Most nitrogen containing compounds have a very positive  G for formation: (e.g. NO, HCN, CH 3 NH 2, CH 3 CN) Amino acids are our foundation; how do we make them chemically? The process of converting N 2 into biologically accessible N is called nitrogen fixation

Nitrogen fixation…. 4 CH 3 COOH + 2N 2 + 2H 2 O  4 H 2 NCH 2 OOH + O 2 (glycine)  G = +564 kJ 2 CH 3 COOH + 2NH 3 + O 2  2 H 2 NCH 2 OOH + 2H 2 O (glycine)  G =  396 kJ

Nitrogen fixation…. Four basic compounds used to create nitrogenous fertilizer: NH 3 HNO 3 NH 4 NO 3 (NH 2 ) 2 CO  G o = negative Ammonia, Nitric acid, Ammonium nitrate, urea

A biochemical use for thermo: n n Mammalian metabolism:   ATP + H 2 O  ADP + H 3 PO 4  G =  31kJ 36ADP + 36H 3 PO 4 + 6O 2 + C 6 H 12 O 6    energy storage) 36ATP + 6CO H 2 O Adenosine triphosphate (ATP)

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

n n example: the production of glutamine 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.

glutamic acid + NH 3  glutamine + H 2 O    G = +  kJnon-spontaneous But… ATP + H 2 O  ADP + H 3 PO 4  G =  31kJ So, if these two systems were coupled… The problem:

  glutamic acid + NH 3  glutamine + H 2 O  G = +  kJ + ATP + H 2 O  ADP + H 3 PO 4  G =  31 kJ glutamic acid + ATP + NH 3  ADP + glutamine + H 3 PO 4  G =  17 kJ This coupling is how many biochemical reaction proceed. It is an example of Hess’ Law. Finish Chapter 14…

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