Chem 12
Unit 1 - Reaction Kinetics
Sec 1.10 PE Diagram for a Reaction Mechanism
teacher
AC (step 1)
see p. 26 SW
AC (step 2)
see p.27
AC (step 3)
see p. 27
HOOBr
PE
HOBr
HBr + O2
STEP 1
STEP 2
STEP 3
H2O + Br2
REACTION PROCEEDS
Notes:





each “bump” is a step
the higher the bump, (greater Ea) the slower the step
the highest bump (from the reactants level) is for the RDS
AC’s at top of bumps, intermediates in middle “valleys”, products in the final “valley”
the Ea for the forward overall rxn. is vertical distance from reactants to top of highest
bump.
On the diagram for this mechanism at the top of the page, label the Rate Determining Step.
Draw an arrow to show the Ea (overall reaction) . Label it. Draw another labeled arrow to show
the Ea for Step 1. Draw a labeled arrow to show  for the overall reaction.
PE
REACTION PROCEEDS
In each of the reactions in the diagram above, the Ea for the overall forward reaction is the
difference in energy between the reactants and the top of the highest peak.
Chem 12
Unit 1 - Reaction Kinetics
Question: Given the following Potential Energy Diagram for a reaction mechanism:
PE
(KJ)
80
70
60
50
Reaction Proceeds
1. This mechanism has
3. Step
steps
is the RDS
5. The overall rxn. is
6.  =
2. Ea for overall rxn =
4. Step
kJ
is the fastest step.
thermic
kJ
7.  for reverse rxn. =
kJ
9. RDS for reverse rxn. is step
Draw a Potential Energy Diagram for a reaction mechanism with 2 steps. The first step is
fast and the second step is slow. The overall reaction is exothermic. and the  for the
forward reaction.
PE
Reaction Proceeds
Read p. 29-30 in SW.
Do Ex. 54 and 55 on page 30 of SW.
Chem 12
Unit 1 - Reaction Kinetics
Sec 1.10 PE Diagram for a Reaction Mechanism
student
AC (step 1)
see p. 26 SW
AC (step 2)
see p.27
AC (step 3)
see p. 27
HOOBr
PE
HOBr
HBr + O2
STEP 1
STEP 2
STEP 3
H2O + Br2
REACTION PROCEEDS
Notes:





each “bump” is a step
the higher the bump, (greater Ea) the slower the step
the highest bump (from the reactants level) is for the RDS
AC’s at top of bumps, intermediates in middle “valleys”, products in the final “valley”
the Ea for the forward overall rxn. is vertical distance from reactants to top of highest
bump.
On the diagram for this mechanism at the top of the page, label the Rate Determining Step.
Draw another labeled arrow to show the Ea for Step 1. Draw a labeled arrow to show  for
the overall reaction.
PE
REACTION PROCEEDS
In each of the reactions in the diagram above, the Ea for the overall forward reaction is the
difference in energy between the reactants and the top of the highest peak.
Chem 12
Unit 1 - Reaction Kinetics
Question: Given the following Potential Energy Diagram for a reaction mechanism:
PE
(KJ)
80
70
60
50
Reaction Proceeds
1. This mechanism has
3. Step
steps
2. Ea for the forwards rxn =
is the RDS
4. Step
thermic 6.  =
5. The overall rxn. is
7.  for reverse rxn. =
kJ
kJ
is the fastest step.
kJ
9. RDS for reverse rxn. is step
Draw a Potential Energy Diagram for a reaction mechanism with 2 steps. The first step is
fast and the second step is slow. The overall reaction is exothermic. Lable the  for the
forward reaction and the Ea for each step.
PE
Reaction Proceeds
Read p. 29-30 in SW.
Do Ex. 54 and 55 on page 30 of SW.