CEM 142 LATEST 2026 EXAM QUESTIONS AND SOLUTIONS
SCORED A+
✔✔Consider a reaction where Rate = k[A][B]. What factor in the rate equation is
temperature dependent?
A. [A]
B. [B]
C. k (the rate constant)
D. All of the above - ✔✔-C
✔✔The rate constant k must change with ______________. - ✔✔-Temperature.
✔✔k = Ae^-Ea/RT
As T increases, what happens to k?
As Ea (activation energy) increases, what happens to k?
A. k increases
B. k decreases
C. k does not change
D. It depends... - ✔✔-Arrhenius Equation.
-A
-B
✔✔k = Ae^-Ea/RT
What does k stand for?
What does Ae stand for?
What does Ea stand for?
What does T stand for? - ✔✔-The rate constant.
-The pre-exponential factor depends on the reaction-gives information about the
number of collisions that lead to reaction.
-As the activation energy increases, the rate constant decreases.
-As T increases the rate constant increases.
✔✔Why do we study kinetics? - ✔✔-To provide information about the reaction
mechanism.
✔✔Reaction Mechanism: - ✔✔-The path from reactants to products.
-The sequence of events-collisions, bond breaking, and bond forming.
-The mechanism may have more than one step (reaction).
-We use kinetic data to probe what is going on.
✔✔What affects the rate of a reaction A--->B?
1. The activation energy.
2. The value of the rate constant.
3. The concentrations of reactants.
4. The concentrations of products.
,A. Yes
B. No
C. It depends - ✔✔-1. A
-2. A
-3. C
-4. B
✔✔The rate law must be determined by _____________. - ✔✔-Experiment.
✔✔If the rate law does not contain a concentration of one of the reactants, what does
that tell you? - ✔✔-That rate does not depend on concentration of one of the reactants if
zero order. Tells that the reaction occurs in multiple steps.
✔✔The reaction rate depends on the height of the...? - ✔✔-Activation energy barrier.
✔✔But what if the reaction energy diagram has more than one energy barrier?
Which barrier determines the rate?
A. Delta G1
B. Delta G2
C. Both Delta G1 and Delta G2
D. Delta Gr - ✔✔-A
✔✔The Rate Equation: Tells you about what reactants are in the _____________
_______________ step (the bottleneck). - ✔✔-Rate Determining.
✔✔For A+B-->C
If the rate = k[A][B], then ________________ present in the TS for the rate determining
step.
IF the rate = k [A], then ______________ present fro the rate determining step. - ✔✔-
Both reactants are
-Only A is
✔✔Use Kinetic Data to Probe Mechanism: Determine rate equation (using any of the
methods discussed). Then...? - ✔✔-Develop a mechanism consistent with the rate
equation.
✔✔A Nucleophilic Substitution:
CH3Br + OH- --> CH3OH + Br-
Rate = k[CH3Br][OH-]
What species must be present in the rate determining step?
A. CH3Br
B. OH-
C. Both CH3Br and OH-
, D. Impossible to tell. - ✔✔-C
*Because both concentrations present in rate law.
✔✔A Nucleophilic Substitution:
CH3Br + OH- --> CH3OH + Br-
Rate = k[CH3Br][OH-]
What would a plausible mechanism be (one that is consistent with the evidence)? - ✔✔-
One step- in which the hydroxide attacks as the Br leaves.
✔✔Another Nucleophilic Substitution:
(CH3)3CBr+OH- --> (CH3)3COH +Br-
Rate = k [(CH3)3CBr]
What species must be present in the rate determining step?
A. (CH3)3CBr
B. OH-
C. Both (CH3)3CBr and OH-
D. Impossible to tell - ✔✔-A
*Because only 1 in rate law above.
*Tells that this does NOT happen all at once.
✔✔Another Nucleophilic Substitution:
(CH3)3CBr+OH- --> (CH3)3COH +Br-
Rate = k [(CH3)3CBr]
What would a plausible mechanism be (one that is consistent with the evidence)? - ✔✔-
A two step mechanism in which the formation of the (+) charged carbon is rate
determining (highest Ea).
✔✔Catalysis: - ✔✔Provide an alternate pathway- with a lower activation energy.
Therefore the reaction goes faster.
✔✔Enzymes: - ✔✔-Induced fit of substrate and enzyme active site (intermolecular
forces promote binding).
-Lowers activation energy of the reaction.
✔✔At equilibrium the rate of the forward reaction _____________ the rate of the
reverse reaction.
There is not further observable change-but both forward and backward reactions are
still _________________. - ✔✔-Equals.
-Continuing.
✔✔Equilibrium Constant for a general reaction nA+mB--><--oC+pD - ✔✔Keq = [C]^O
[D]^P / [A]^n [B]^m
*Products are on top and Reactants on the bottom.
*Each concentration is raised to the power of its coefficient in the balanced reaction.
SCORED A+
✔✔Consider a reaction where Rate = k[A][B]. What factor in the rate equation is
temperature dependent?
A. [A]
B. [B]
C. k (the rate constant)
D. All of the above - ✔✔-C
✔✔The rate constant k must change with ______________. - ✔✔-Temperature.
✔✔k = Ae^-Ea/RT
As T increases, what happens to k?
As Ea (activation energy) increases, what happens to k?
A. k increases
B. k decreases
C. k does not change
D. It depends... - ✔✔-Arrhenius Equation.
-A
-B
✔✔k = Ae^-Ea/RT
What does k stand for?
What does Ae stand for?
What does Ea stand for?
What does T stand for? - ✔✔-The rate constant.
-The pre-exponential factor depends on the reaction-gives information about the
number of collisions that lead to reaction.
-As the activation energy increases, the rate constant decreases.
-As T increases the rate constant increases.
✔✔Why do we study kinetics? - ✔✔-To provide information about the reaction
mechanism.
✔✔Reaction Mechanism: - ✔✔-The path from reactants to products.
-The sequence of events-collisions, bond breaking, and bond forming.
-The mechanism may have more than one step (reaction).
-We use kinetic data to probe what is going on.
✔✔What affects the rate of a reaction A--->B?
1. The activation energy.
2. The value of the rate constant.
3. The concentrations of reactants.
4. The concentrations of products.
,A. Yes
B. No
C. It depends - ✔✔-1. A
-2. A
-3. C
-4. B
✔✔The rate law must be determined by _____________. - ✔✔-Experiment.
✔✔If the rate law does not contain a concentration of one of the reactants, what does
that tell you? - ✔✔-That rate does not depend on concentration of one of the reactants if
zero order. Tells that the reaction occurs in multiple steps.
✔✔The reaction rate depends on the height of the...? - ✔✔-Activation energy barrier.
✔✔But what if the reaction energy diagram has more than one energy barrier?
Which barrier determines the rate?
A. Delta G1
B. Delta G2
C. Both Delta G1 and Delta G2
D. Delta Gr - ✔✔-A
✔✔The Rate Equation: Tells you about what reactants are in the _____________
_______________ step (the bottleneck). - ✔✔-Rate Determining.
✔✔For A+B-->C
If the rate = k[A][B], then ________________ present in the TS for the rate determining
step.
IF the rate = k [A], then ______________ present fro the rate determining step. - ✔✔-
Both reactants are
-Only A is
✔✔Use Kinetic Data to Probe Mechanism: Determine rate equation (using any of the
methods discussed). Then...? - ✔✔-Develop a mechanism consistent with the rate
equation.
✔✔A Nucleophilic Substitution:
CH3Br + OH- --> CH3OH + Br-
Rate = k[CH3Br][OH-]
What species must be present in the rate determining step?
A. CH3Br
B. OH-
C. Both CH3Br and OH-
, D. Impossible to tell. - ✔✔-C
*Because both concentrations present in rate law.
✔✔A Nucleophilic Substitution:
CH3Br + OH- --> CH3OH + Br-
Rate = k[CH3Br][OH-]
What would a plausible mechanism be (one that is consistent with the evidence)? - ✔✔-
One step- in which the hydroxide attacks as the Br leaves.
✔✔Another Nucleophilic Substitution:
(CH3)3CBr+OH- --> (CH3)3COH +Br-
Rate = k [(CH3)3CBr]
What species must be present in the rate determining step?
A. (CH3)3CBr
B. OH-
C. Both (CH3)3CBr and OH-
D. Impossible to tell - ✔✔-A
*Because only 1 in rate law above.
*Tells that this does NOT happen all at once.
✔✔Another Nucleophilic Substitution:
(CH3)3CBr+OH- --> (CH3)3COH +Br-
Rate = k [(CH3)3CBr]
What would a plausible mechanism be (one that is consistent with the evidence)? - ✔✔-
A two step mechanism in which the formation of the (+) charged carbon is rate
determining (highest Ea).
✔✔Catalysis: - ✔✔Provide an alternate pathway- with a lower activation energy.
Therefore the reaction goes faster.
✔✔Enzymes: - ✔✔-Induced fit of substrate and enzyme active site (intermolecular
forces promote binding).
-Lowers activation energy of the reaction.
✔✔At equilibrium the rate of the forward reaction _____________ the rate of the
reverse reaction.
There is not further observable change-but both forward and backward reactions are
still _________________. - ✔✔-Equals.
-Continuing.
✔✔Equilibrium Constant for a general reaction nA+mB--><--oC+pD - ✔✔Keq = [C]^O
[D]^P / [A]^n [B]^m
*Products are on top and Reactants on the bottom.
*Each concentration is raised to the power of its coefficient in the balanced reaction.
