Outline: 1/29/07

Turn in Seminar reports – to me Today: Student Research Symposium

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 Hrxn, phase change problems S calculations: T S = q Go

rxn = Horxn TSo

rxn problems Since Ho

rxn and Sorxn are relatively

independent of temperature: GT

rxn Horxn TSo

rxn

Worksheet #3: N2O4(g) 2 NO2(g)

colorless brown Go = G(prdts) G(rctnts) = 2 5198 = +4 kJ (not spontaneous)

G77 = rxn Srxn )

= 5777 0.176) = +43 kJ (really not spontaneous!)

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?

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:

Srxn = Sorxn 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.

Grxn = Gorxn RT lnQ

where Q = reaction quotient = [prods]/[rcts]

Since : GT

rxn = Hrxn T Srxn

Then: GT

rxn = Horxn T(So

rxn R ln Q)

Or:

Worksheet #2 (cont’d): N2O4(g) 2 NO2(g)

colorless brown What is Q? = (pNO2 )2/(pN2O4)

Q = 0.1 and Grxn = kJ 0.008314 (298) ln 0.1

= 4 7 1.7 kJ (spontaneous!)

Assume pNO2 = pN2O4 = 0.1 atm

Summary of Thermo: E, H, S and G are defined First law calculations: E = q + w Hrxn, phase change problems S calculations: T S = q GT

rxn Horxn TSo

rxn problems Grxn = Go

rxn RTlnQ problems

Let’s see how we’re doing…

Which of the following has the largest So?

1. HCl (l)

2. HCl (s)

3. HCl (g)

4. HI (g)

5. HBr (g)

11 22 33 44 55

What is the G at 100°C for a reaction that has Ho = 271 kJ/mol & So = +11.2 J/K?

1 272 kJ/mol

2 1391 kJ/mol

3 275 kJ/mol

4449 kJ/mol

282 kJ/mol

11 22 33 44 55

Summary of Thermo: E, H, S and G are defined Heat capacity problems: q = n Cp T First law calculations: E = q + w Hrxn, phase change problems S calculations: T S = q GT

rxn Horxn TSo

rxn problems Grxn = Go

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 (NN) is very stable thermodynamically….

Most nitrogen containing compounds have a very positive G 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

Nitrogen fixation….4 CH3COOH + 2N2 + 2H2O

4 H2NCH2OOH + O2

(glycine)

G = +564 kJ 2 CH3COOH + 2NH3 + O2

2 H2NCH2OOH + 2H2O

(glycine)

G = 396 kJ

Nitrogen fixation….Four basic compounds used to create

nitrogenous fertilizer:

NH3 HNO3 NH4NO3 (NH2)2CO

Go = negative

Ammonia, Nitric acid,

Ammonium nitrate, urea

A biochemical use for thermo: Mammalian metabolism: ATP + H2O ADP + H3PO4 G = 31kJ 36ADP + 36H3PO4 + 6O2 + C6H12O6

energy storage) 36ATP + 6CO2 + 42H2O

Adenosine triphosphate (ATP)

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

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 + NH3 glutamine + H2OG = +1kJnon-spontaneous

But…ATP + H2O ADP + H3PO4 G = 31kJ

So, if these two systems were coupled…

The problem:

glutamic acid + NH3 glutamine + H2O G = +1kJ

+ ATP + H2O ADP + H3PO4 G = 31 kJ

glutamic acid + ATP + NH3 ADP + glutamine + H3PO4

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, 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!