1. Rate Laws

2. Rate of Reaction rate = amount/(time x “volume”) amount [=] mol, g
time [=] s, min, h
“volume” [=] L (dm3), kg cat, m2 cat
rA = mol/s/L
rA’ = mol/s/g
rA” = mol/s/m2

3. Generic Reaction aA + bB  cC + dD Elementary (irreversible)
-rA = k CAa CBb
Elementary (reversible)
-rA = kf CAa CBb – kr CCc CDd

4. Complex -rA = k1 CA/(1+k2 CA)
Generic Reaction
aA + bB  cC + dD
1st Order -rA = k CA
2nd Order -rA = k CA2
Power Law -rA = CAa CBb
Complex -rA = k1 CA/(1+k2 CA)
So how do we know?
Experiment!

5. Generic Reaction aA + bB  cC + dD
Assume experiment shows reaction is elementary and irreversible:
-rA = k CAa CBb
Now, rewrite the stoichiometric equation:
A + (b/a)B  (c/a)C + (d/a)D
What is rate law?

6. So what about the rate constant?
Arrhenius Equation
k = A exp(-Ea/RT)
ln k = ln A – Ea/RT
m = -Ea/RT
Y = b mX
Y = ln k
X = 1/T

7. OK, what is this activation energy?

8. OK, what is this activation energy?AB P
A + B

9. Firefly Flashing Frequency
T (oC) 21 25 30
Flashes/ min
9.0
12.16
16.2

10. Evidently, an activated process!