AP Chemistry : Thermochemistry and Kinetics
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Example Questions
Example Question #1 : Laws Of Thermodynamics
A chemistry student is trying to calculate how long it will take a power source of 
There is not enough information to determine the amount of time needed for the process described
In order to solve this problem, we'll need to break it up into steps.
Step 1: Calculate the amount of energy necessary to raise the sample of ice from 
Step 2: Calculate the amount of energy necessary to convert the sample at 
Step 3: Calculate the amount of energy necessary to convert the sample of water from 
Step 4: Sum the amount of energy from the previous 3 steps. This value is the total amount of energy for the entire process.
Step 5: Now that we know the total amount of energy needed for the process, we need to calculate the time based on the amount of power provided.
Example Question #2 : Help With Rate Determining Steps
The overall reaction can only proceed as quickly as the __________.
catalyst is added
intermediate is decomposed
products are removed
rate-determining step
rate-determining step
The rate-determining step in a reaction mechanism is a kinetic bottleneck, in that it prevents the overall reaction from proceeding; thus, it is what determines how quickly the overall reaction can proceed.
Example Question #31 : Kinetics And Energy
Which of the following does not affect a forward reaction rate?
Medium
Product concentration
Catalysts
Temperature
Product concentration
Product concentration would not affect a forward reaction rate, since that is what is being formed. Catalysts specifically speed up reaction rates, as does temperature. Medium can also affect reaction rate because some molecules are more likely to react with each other in certain environments.
Example Question #1 : Principles Of Reaction Kinetics
Which of the following is not true of the transition state?
Old bonds are weakened and new bonds begin to form
It has a greater energy than the reactants
It has a greater energy than the products
It cannot dissociate into products without needing any additional energy
It cannot dissociate into products without needing any additional energy
The transition state is the energy barrier in a reaction—energy is needed to reach this state. Once it is acheived, however, it can either revert back to reactants or dissociate into products without any added energy.
Example Question #1 : Principles Of Reaction Kinetics
Which of the following is true:
I. First order reactions proceed at a constant rate
II. First order reactions have a constant half-life
III. First order reactions have one reactant
I only
II and III
II only
I, II, and III
II only
First order reactions have the rate equation 
The half-life equation is 
Lastly, the overall reaction can have any number of reactants. A reaction is first order because its rate-limiting step has only one reactant.
Only statement II is true.
Example Question #2 : Principles Of Reaction Kinetics
The following reversible reaction takes place in a closed container:
The system is allowed to reach equilibrium before 2 moles of reactant A are added to the container.
The net rate of formation of product B immediately following the addition of reactant A is __________.
zero
impossible to determine without additional information
negative
positive
positive
According to Le Chatelier's principle, an increase in the concentration of reactants will cause the reaction to shift to the right in order to re-establish equilibrium. Thus, immediately after reactant A is added, the forward reaction will increase and the net rate of formation of the products will be positive.
Example Question #4 : Principles Of Reaction Kinetics
Rate data is collected for a reaction, and the following integrated rate law is derived.
If this reaction is __________ with respect to reactant A, a plot of ln[A] versus time would be __________.
first order . . . linear
first order . . . parabolic
second order . . . parabolic
zero order . . . linear
first order . . . linear
The integrated rate law shown is for a reaction rate law with a first-order dependence on reactact A. If such a rate law accurately describes the kinetics of the reaction, then ln[A] will vary linearly with respect to time.
Example Question #5 : Principles Of Reaction Kinetics
Which of the following affects the rate of a reaction?
Collision orientation
Molecules' energies
All of these
Frequency of collision
All of these
Since reactant molecules collide and interact to break old bond and form new ones, any factors affecting collision and interactions will affect the reaction rate. Thus, increasing temperature will increase both the frequency of collisions and the average kinetic energy of the molecules. Enzymes bring molecules close to each other and orient them in a way that facilitates reactions.
Example Question #1 : Integrated Rate Laws
The rate constant for a second-order reaction is 0.15 M-1s-1. If the initial concentration of the reactant is 0.30 M, how long does it take for the concentration to decrease to 0.15 M?
88.8 seconds
253 second
44.4 second
22.2 seconds
11.1 seconds
22.2 seconds
Example Question #1 : Integrated Rate Laws
Based on the figure above, what is the order of reaction?
Third Order
Squared Order
First order
Second Order
Zero Order
First order
For a first order reaction, the ln [A]t is linear with t.
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