Reaction Mechanisms and Rate Law - AP Chemistry
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What is the molecularity of an elementary step $A + 2B \rightarrow AB_2$?
What is the molecularity of an elementary step $A + 2B \rightarrow AB_2$?
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Termolecular. Count total molecules: 1 A + 2 B = 3 molecules.
Termolecular. Count total molecules: 1 A + 2 B = 3 molecules.
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What is a termolecular reaction?
What is a termolecular reaction?
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A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
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Which step in a reaction mechanism is the rate-determining step?
Which step in a reaction mechanism is the rate-determining step?
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The slowest step. This step controls the overall reaction rate.
The slowest step. This step controls the overall reaction rate.
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How do you find the overall order of a reaction?
How do you find the overall order of a reaction?
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Sum the exponents in the rate law. Add all concentration exponents in rate law.
Sum the exponents in the rate law. Add all concentration exponents in rate law.
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What is the term for a species that appears in the mechanism but not in the overall reaction?
What is the term for a species that appears in the mechanism but not in the overall reaction?
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Intermediate. Formed during mechanism but cancels out overall.
Intermediate. Formed during mechanism but cancels out overall.
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Determine the rate law for the elementary reaction $2NO + O_2 \rightarrow 2NO_2$.
Determine the rate law for the elementary reaction $2NO + O_2 \rightarrow 2NO_2$.
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Rate = $k[NO]^2[O_2]$. For elementary reactions, stoichiometry equals rate law exponents.
Rate = $k[NO]^2[O_2]$. For elementary reactions, stoichiometry equals rate law exponents.
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What is the role of a catalyst in a reaction mechanism?
What is the role of a catalyst in a reaction mechanism?
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It lowers the activation energy, increasing reaction rate. Provides alternative pathway with lower energy barrier.
It lowers the activation energy, increasing reaction rate. Provides alternative pathway with lower energy barrier.
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What is meant by the term 'elementary step' in a reaction mechanism?
What is meant by the term 'elementary step' in a reaction mechanism?
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A single reaction step with a single transition state. Cannot be broken down into simpler mechanistic steps.
A single reaction step with a single transition state. Cannot be broken down into simpler mechanistic steps.
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What is an elementary reaction?
What is an elementary reaction?
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A reaction that occurs in a single step. Proceeds directly without intermediate steps.
A reaction that occurs in a single step. Proceeds directly without intermediate steps.
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Find and state the overall order of reaction for Rate = $k[A][B]^2$.
Find and state the overall order of reaction for Rate = $k[A][B]^2$.
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- Add all exponents: $1 + 2 = 3$.
- Add all exponents: $1 + 2 = 3$.
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What is a termolecular reaction?
What is a termolecular reaction?
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A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
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What is the overall reaction order if Rate = $k[A]^0[B]^1$?
What is the overall reaction order if Rate = $k[A]^0[B]^1$?
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- Sum exponents: $0 + 1 = 1$.
- Sum exponents: $0 + 1 = 1$.
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What is a catalyst?
What is a catalyst?
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A substance that increases the reaction rate without being consumed. Speeds up reaction but remains unchanged overall.
A substance that increases the reaction rate without being consumed. Speeds up reaction but remains unchanged overall.
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Identify the molecularity of a single-step reaction involving two reactants.
Identify the molecularity of a single-step reaction involving two reactants.
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Bimolecular. Two reactants means molecularity equals 2.
Bimolecular. Two reactants means molecularity equals 2.
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Define activation energy in the context of a reaction mechanism.
Define activation energy in the context of a reaction mechanism.
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The minimum energy required for a reaction to occur. Energy barrier that must be overcome for reaction.
The minimum energy required for a reaction to occur. Energy barrier that must be overcome for reaction.
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Identify the term for a reaction step that involves a single reactant.
Identify the term for a reaction step that involves a single reactant.
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Unimolecular. Only one molecule undergoes reaction in the step.
Unimolecular. Only one molecule undergoes reaction in the step.
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What units does the rate constant $k$ have for a zero-order reaction?
What units does the rate constant $k$ have for a zero-order reaction?
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$M\cdot s^{-1}$. Zero-order has units of concentration per time.
$M\cdot s^{-1}$. Zero-order has units of concentration per time.
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State the units of the rate constant $k$ for a second-order reaction.
State the units of the rate constant $k$ for a second-order reaction.
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$M^{-1}s^{-1}$. Second-order reactions have units of reciprocal concentration per time.
$M^{-1}s^{-1}$. Second-order reactions have units of reciprocal concentration per time.
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What is the molecularity of an elementary step $A + 2B \rightarrow AB_2$?
What is the molecularity of an elementary step $A + 2B \rightarrow AB_2$?
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Termolecular. Count total molecules: 1 A + 2 B = 3 molecules.
Termolecular. Count total molecules: 1 A + 2 B = 3 molecules.
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Predict the rate law for the elementary reaction $A_2 + B \rightarrow A_2B$.
Predict the rate law for the elementary reaction $A_2 + B \rightarrow A_2B$.
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Rate = $k[A_2][B]$. Stoichiometry directly gives rate law for elementary steps.
Rate = $k[A_2][B]$. Stoichiometry directly gives rate law for elementary steps.
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What is the order of reaction with respect to $A$ if Rate = $k[A]^2$?
What is the order of reaction with respect to $A$ if Rate = $k[A]^2$?
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- The exponent of $[A]$ indicates second order with respect to $A$.
- The exponent of $[A]$ indicates second order with respect to $A$.
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What is the difference between an intermediate and a catalyst in a reaction mechanism?
What is the difference between an intermediate and a catalyst in a reaction mechanism?
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Intermediates are produced and consumed; catalysts are not consumed. Key distinction: intermediates appear then disappear in the mechanism.
Intermediates are produced and consumed; catalysts are not consumed. Key distinction: intermediates appear then disappear in the mechanism.
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What is the rate law for the elementary reaction $2A \rightarrow A_2$?
What is the rate law for the elementary reaction $2A \rightarrow A_2$?
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Rate = $k[A]^2$. Stoichiometry gives exponents for elementary reactions.
Rate = $k[A]^2$. Stoichiometry gives exponents for elementary reactions.
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Determine the rate law for a unimolecular reaction involving $A$.
Determine the rate law for a unimolecular reaction involving $A$.
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Rate = $k[A]$. Unimolecular means first order in the single reactant.
Rate = $k[A]$. Unimolecular means first order in the single reactant.
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What is a termolecular reaction?
What is a termolecular reaction?
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A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.
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Which step in a reaction mechanism is the rate-determining step?
Which step in a reaction mechanism is the rate-determining step?
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The slowest step. This step controls the overall reaction rate.
The slowest step. This step controls the overall reaction rate.
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How do you find the overall order of a reaction?
How do you find the overall order of a reaction?
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Sum the exponents in the rate law. Add all concentration exponents in rate law.
Sum the exponents in the rate law. Add all concentration exponents in rate law.
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Find and state the overall order of reaction for Rate = $k[A][B]^2$.
Find and state the overall order of reaction for Rate = $k[A][B]^2$.
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- Add all exponents: 1 + 2 = 3.
- Add all exponents: 1 + 2 = 3.
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What is the term for a species that appears in the mechanism but not in the overall reaction?
What is the term for a species that appears in the mechanism but not in the overall reaction?
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Intermediate. Formed during mechanism but cancels out overall.
Intermediate. Formed during mechanism but cancels out overall.
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Determine the rate law for the elementary reaction $2NO + O_2 \rightarrow 2NO_2$.
Determine the rate law for the elementary reaction $2NO + O_2 \rightarrow 2NO_2$.
Tap to reveal answer
Rate = $k[NO]^2[O_2]$. For elementary reactions, stoichiometry equals rate law exponents.
Rate = $k[NO]^2[O_2]$. For elementary reactions, stoichiometry equals rate law exponents.
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