AP Chemistry Flashcards: Reaction Mechanisms And Rate Law

What this deck covers

This deck focuses on Reaction Mechanisms And Rate Law, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: How do you find the overall order of a reaction?

Answer: Sum the exponents in the rate law. Add all concentration exponents in rate law.

Flashcard 2: What is the overall reaction order if Rate = $k[A]^0[B]^1$?

Answer:

1. Sum exponents: 0 + 1 = 1.

Flashcard 3: What is the rate law expression for a reaction $aA + bB \rightarrow cC$?

Answer: Rate = $k[A]^m[B]^n$. General form where m and n are determined experimentally, not from coefficients.

Flashcard 4: State the units of the rate constant $k$ for a first-order reaction.

Answer: $s^{-1}$. First-order reactions have units of reciprocal time.

Flashcard 5: Define the term 'reaction mechanism'.

Answer: A series of elementary steps that describe the pathway from reactants to products. Shows how reactants transform through specific elementary steps.

Flashcard 6: What is a termolecular reaction?

Answer: A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.

Flashcard 7: What is the order of reaction with respect to $A$ if Rate = $k[A]^2$?

Answer:

1. The exponent of $[A]$ indicates second order with respect to $A$.

Flashcard 8: Predict the rate law for the elementary reaction $A_2 + B \rightarrow A_2B$.

Answer: Rate = $k[A_2][B]$. Stoichiometry directly gives rate law for elementary steps.

Flashcard 9: For a reaction Rate = $k[A]^3$, what is the overall reaction order?

Answer:

1. Single exponent gives overall order directly.

Flashcard 10: What is a reaction intermediate?

Answer: A species formed and consumed during the reaction mechanism. Temporary species that doesn't appear in overall equation.

Flashcard 11: What is the term for a species that appears in the mechanism but not in the overall reaction?

Answer: Intermediate. Formed during mechanism but cancels out overall.

Flashcard 12: For a reaction Rate = $k[A]^1[B]^2$, what is the reaction order with respect to $B$?

Answer:

1. The exponent of [B] in the rate law.

Flashcard 13: What is the role of the rate-determining step in a reaction mechanism?

Answer: Controls the overall rate of the reaction. Determines how fast products form overall.

Flashcard 14: Define activation energy in the context of a reaction mechanism.

Answer: The minimum energy required for a reaction to occur. Energy barrier that must be overcome for reaction.

Flashcard 15: How does a catalyst affect the rate-determining step?

Answer: It lowers the activation energy of the rate-determining step. Reduces energy barrier of the limiting step.

Flashcard 16: For Rate = $k[A]^2[B]^0$, what is the order with respect to $B$?

Answer:

1. Zero exponent means B doesn't affect rate.

Flashcard 17: What is the difference between an intermediate and a catalyst in a reaction mechanism?

Answer: Intermediates are produced and consumed; catalysts are not consumed. Key distinction: intermediates appear then disappear in the mechanism.

Flashcard 18: What is an elementary reaction?

Answer: A reaction that occurs in a single step. Proceeds directly without intermediate steps.

Flashcard 19: What is the relationship between rate law and reaction mechanism?

Answer: The rate law can provide insights into the mechanism, particularly the rate-determining step. Rate law reflects the slowest step's kinetics.

Flashcard 20: State the units of the rate constant $k$ for a second-order reaction.

Answer: $M^{-1}s^{-1}$. Second-order reactions have units of reciprocal concentration per time.

Flashcard 21: What is the molecularity of a single elementary step involving three molecules?

Answer: Termolecular. Three molecules participate in a single elementary step.

Flashcard 22: Identify the term for a reaction step that involves a single reactant.

Answer: Unimolecular. Only one molecule undergoes reaction in the step.

Flashcard 23: What is a catalyst?

Answer: A substance that increases the reaction rate without being consumed. Speeds up reaction but remains unchanged overall.

Flashcard 24: Which step in a reaction mechanism is the rate-determining step?

Answer: The slowest step. This step controls the overall reaction rate.

Flashcard 25: In a reaction mechanism, what does the term 'elementary step' imply?

Answer: Each step represents a single molecular event. Each step occurs as written without sub-steps.

Flashcard 26: What is the rate law for the elementary reaction $2A \rightarrow A_2$?

Answer: Rate = $k[A]^2$. Stoichiometry gives exponents for elementary reactions.

Flashcard 27: What is meant by the term 'elementary step' in a reaction mechanism?

Answer: A single reaction step with a single transition state. Cannot be broken down into simpler mechanistic steps.

Flashcard 28: What is a termolecular reaction?

Answer: A reaction involving three reacting species in one step. Rare due to low probability of three-body collisions.

Flashcard 29: What is the first step in writing a reaction mechanism?

Answer: Identify the overall balanced chemical equation. Foundation for proposing elementary steps.

Flashcard 30: What is the purpose of a reaction mechanism?

Answer: To provide a detailed step-by-step description of a reaction. Explains the molecular pathway from reactants to products.

Flashcard 31: State the rate law for a bimolecular elementary reaction involving $A$ and $B$.

Answer: Rate = $k[A][B]$. Elementary steps follow stoichiometry in rate laws.

Flashcard 32: What units does the rate constant $k$ have for a zero-order reaction?

Answer: $M\cdot s^{-1}$. Zero-order has units of concentration per time.

Flashcard 33: Find and state the overall order of reaction for Rate = $k[A][B]^2$.

Answer:

1. Add all exponents: $1 + 2 = 3$.

Flashcard 34: What are the units of the rate constant $k$ for a third-order reaction?

Answer: $M^{-2}s^{-1}$. Third-order has units $M^{-2}s^{-1}$.

Flashcard 35: What is a unimolecular reaction?

Answer: A reaction involving one reactant molecule in a single step. Single molecule breaks down or rearranges.

Flashcard 36: What is the role of a catalyst in a reaction mechanism?

Answer: It lowers the activation energy, increasing reaction rate. Provides alternative pathway with lower energy barrier.

Flashcard 37: Determine the rate law for the elementary reaction $2NO + O_2 \rightarrow 2NO_2$.

Answer: Rate = $k[NO]^2[O_2]$. For elementary reactions, stoichiometry equals rate law exponents.

Flashcard 38: Identify the molecularity of a reaction with the elementary step $A + B \rightarrow C$.

Answer: Bimolecular. Two different molecules react in one step.

Flashcard 39: Identify the molecularity of a single-step reaction involving two reactants.

Answer: Bimolecular. Two reactants means molecularity equals 2.

Flashcard 40: Determine the rate law for a unimolecular reaction involving $A$.

Answer: Rate = $k[A]$. Unimolecular means first order in the single reactant.

Flashcard 41: What is the molecularity of an elementary step $A + 2B \rightarrow AB_2$?

Answer: Termolecular. Count total molecules: 1 A + 2 B = 3 molecules.