Kinetics

Question 1

Arrhenius equation

Question 2

Mean speed of gases, mean relative speed of gases

Question 3

Derivation of collision rate equation

Question 4

Steric factor

Answer 4

Ratio of A(experiment)/A(collision theory)

Question 5

Ways to obtain kinetic data

Answer 5

1. Light absorbance over time (Beer-Lambert)
2. Conductivity over time
3. Gas pressure over time
4. Electrodes (compare to standard potential with Nernst eqn)
5. Chemical data
   * Titrations
   * Gas chromatogram/mass spec (separates and identifies molecules)

Question 6

Ways to study fast reactions

Answer 6

1. Continuous flow
   * Reagents flow into a tube separately and mix
   * Time proportional to distance along tube (velocity) so conc can be measured over different distances
2. Stopped flow
   * Reagents flow into tube separately and mix
   * Push a plunger back until it hits a stop, flow is stopped and measurement taken
3. Flash photolysis
   * Mixture pulsed with a laser to generate radicals
   * No mixing problem as reagents generated in situ
   * Rapid detection needed

Question 7

Pre-equilibrium hypothesis

Answer 7

• For the rate-determining (slow) step, reagents often in equilibrium with products
• Can help simplify overall rate laws

Question 8

Steady state hypothesis

Answer 8

• Used for intermediates which do not accumulate (react the moment they are produced)
• Can set d[I]/dt = 0

Question 9

Michaelis-Menten equation

Answer 9

1. E+S -> ES
   -1. ES -> E+S
2. ES ->P+E

[E]=[E]0 - [ES]
Substitute into rate equation 2 (rds)
Rearrange for [ES]
Overall rate = k2[ES]

Divide top and bottom by k1 to get MME

k2[E]0 = Vmax