Kinetics-studies the RATES at which reactions occur.
Rate-can only be determined experimentally-data table
Average Rate = Δ[ ]/Δt mol/L·s or M/s
Time(sec)
3.0
7.0
What is the average rate for D?
[D] (M)
0.00470
0.00635
(4.1x10-4mol/L•s)
At one point, the rate of disappearance of N2O was 1.3 x 10M/s, what is the rate of the appearance of O2 at this point?
2N2O  2N2 + O2
3
(6.5x10-4mol/L•s)
Rate Laws
Zero order-changing the [ ] of the reaction has NO effect on
the rate.
1st Order-double the [ ], double the rate
2x=2
x=1
2nd Order-double the [ ]. Rate increases by 4. 2x=4 x=2
Rate =k [ ]
[ ]=mol/L, rate=mol/L·s
Unit on k?
Zero Order rate=k
k=mol/L·s
1st Order
rate=k[ ]
k=sec-1
2nd Order
rate=k[ ]2
k=L/mol·s
3rd Order
rate=k[ ]3
k=L2/mol2·sec
Determine the order of each reactant, overall order of the
reaction, and units on k.
A) Rate=k[NO]2[O2]
B) Rate=k[O3]2[O2]-1
(3rd order-L2/mol2·sec)
(1st order- k=sec-1)
Exp.
[A]
1
2
3
.20
.20
.40
Exp.
[x](mol/L)
1
2
3
4
0.00345
0.00345
0.00690
0.01035
[B]
.20
.40
.20
Rate=k[A]2
[Y](mol/L)
0.00444
0.00888
0.01332
0.01776
Rate=k[x]2[y]
Initial
Rate(M/s)
1x10-3
1x10-3
4x10-3
Initial
rate(M/s)
23.45
46.95
281.4
844.2
The rate law for the reaction 2A+ BC was found to be
rate=k[A][B]2. If the conc. of B is tripled, what will happen to
the rate of the reaction?
(9 times faster)
Exp.
Initial [NO2]
Initial rate(M/s)
1
0.010
7.1x10-5
2
0.020
28x10-5
For the reaction 2NO2 2NO + O2, what is the value of k in
the rate law?
Include units.
(k=0.71 L/mol•sec)
Half-life – 1st order only
t1/2=.693/k
ln[A]t-ln[A]0=-kt
2N2O54N2O +O2
k=4.80x10-4s-1
2.50x10-3M N2O5 is allowed to decompose for 10.0min. What is
the new conc. of N2O5?
(1.9x10-3M)
2H2O2 2H2O + O2
1st order reaction with a half-life of 18min. Initial conc. of
H2O2=0.80M. What is the new concentration after it
decomposes for 72.0min?
(0.05M)
2NO + Cl2  2NOCl
Step 1) NO + Cl2  NOCl2
Step 2) NO + NOCl2 2NOCl
fast eq
slow
(Rate=k[NO]2[Cl2])
Arrhenius equation-relationship between rate constant and
temperature.
ln k = -Ea/RT + lnA
slope= -Ea/R
ln k
1/T
Collision Theory-the reaction rate is equal to the frequency of
effective collisions between reactants. For a collision to be
effective, the molecules must collide with sufficient energy and
in the proper orientation so that products can form.