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AP Chemistry Flashcards: Elementary Reactions

Study Elementary Reactions in AP Chemistry with focused flashcards that help you recognize the idea, recall the key rule, and apply it in practice-style prompts.

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What this deck covers

This deck focuses on Elementary Reactions, 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.

AP Chemistry Flashcards: Elementary Reactions

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QUESTION

Find the net reaction for: A+B→IA+B \rightarrow IA+B→I; I+C→DI+C \rightarrow DI+C→D.

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ANSWER

A+B+C→DA+B+C \rightarrow DA+B+C→D. Add steps and cancel intermediate III.

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Flashcard 1: Find the net reaction for: A+B→IA+B \rightarrow IA+B→I; I+C→DI+C \rightarrow DI+C→D.

Answer: A+B+C→DA+B+C \rightarrow DA+B+C→D. Add steps and cancel intermediate III.

Flashcard 2: What is the definition of an intermediate in a reaction mechanism?

Answer: Formed in one step and consumed in a later step. Intermediates don't appear in reactants or products of overall reaction.

Flashcard 3: What is the molecularity of an elementary step with one reactant particle?

Answer: Unimolecular. One molecule participates in the elementary step.

Flashcard 4: What is the definition of an elementary reaction step in a mechanism?

Answer: A single-step molecular event with no intermediates. Elementary steps occur in one collision without breaking into smaller steps.

Flashcard 5: What is the rate law for the unimolecular elementary step A→A \rightarrowA→ products?

Answer: rate=k[A]\text{rate}=k[A]rate=k[A]. For elementary steps, rate law exponents equal stoichiometric coefficients.

Flashcard 6: What is the rate law for the bimolecular elementary step A+B→A+B \rightarrowA+B→ products?

Answer: rate=k[A][B]\text{rate}=k[A][B]rate=k[A][B]. Each reactant appears to the first power in bimolecular steps.

Flashcard 7: What is the rate law for the bimolecular elementary step 2A→2A \rightarrow2A→ products?

Answer: rate=k[A]2\text{rate}=k[A]^2rate=k[A]2. Coefficient 2 becomes exponent 2 in elementary rate laws.

Flashcard 8: What is the rate law for the termolecular elementary step 2A+B→2A+B \rightarrow2A+B→ products?

Answer: rate=k[A]2[B]\text{rate}=k[A]^2[B]rate=k[A]2[B]. Exponents match stoichiometric coefficients for elementary steps.

Flashcard 9: What is the overall reaction order for an elementary step with rate law rate=k[A]2[B]\text{rate}=k[A]^2[B]rate=k[A]2[B]?

Answer: 333. Sum all exponents: 2+1=32 + 1 = 32+1=3.

Flashcard 10: Identify the units of kkk for an elementary step with rate=k[A]\text{rate}=k[A]rate=k[A].

Answer: s−1\text{s}^{-1}s−1. First-order reactions have units of inverse time.

Flashcard 11: Identify the units of kkk for an elementary step with rate=k[A][B]\text{rate}=k[A][B]rate=k[A][B].

Answer: M−1s−1\text{M}^{-1}\text{s}^{-1}M−1s−1. Second-order overall requires one inverse concentration unit.

Flashcard 12: Identify the units of kkk for an elementary step with rate=k[A]2[B]\text{rate}=k[A]^2[B]rate=k[A]2[B].

Answer: M−2s−1\text{M}^{-2}\text{s}^{-1}M−2s−1. Third-order overall requires two inverse concentration units.

Flashcard 13: What is the definition of a catalyst in a reaction mechanism?

Answer: Consumed early and regenerated later; not in net equation. Catalysts appear in mechanism but not in overall equation.

Flashcard 14: What is the definition of the rate-determining step (RDS) in a mechanism?

Answer: The slowest step that limits the overall rate. All other steps must wait for the slowest step to complete.

Flashcard 15: What is the relationship between the RDS and the observed rate law in many mechanisms?

Answer: Observed rate law often matches the RDS rate law. The RDS controls the overall reaction rate.

Flashcard 16: Which species cancels when you add elementary steps to obtain the overall reaction?

Answer: Intermediates (and catalysts) cancel from the net equation. Species produced and consumed in mechanism don't appear in net equation.

Flashcard 17: Identify the intermediate from the mechanism: A+B→IA+B \rightarrow IA+B→I; I+C→I+C \rightarrowI+C→ products.

Answer: III. Produced in step 1, consumed in step 2.

Flashcard 18: What is the predicted rate law if the slow elementary step is A+B→A+B \rightarrowA+B→ products?

Answer: rate=k[A][B]\text{rate}=k[A][B]rate=k[A][B]. Elementary step rate laws directly reflect stoichiometry.

Flashcard 19: What is the molecularity of an elementary step with three reactant particles?

Answer: Termolecular (rare). Three-body collisions are statistically unlikely.

Flashcard 20: What is the molecularity of an elementary step with two reactant particles?

Answer: Bimolecular. Two molecules collide in the elementary step.

Flashcard 21: What is the overall reaction obtained by adding these steps: A+B→CA+B \rightarrow CA+B→C and C+D→EC+D \rightarrow EC+D→E?

Answer: A+B+D→EA+B+D \rightarrow EA+B+D→E. Add steps and cancel intermediate C on both sides.

Flashcard 22: What is the molecularity of an elementary step?

Answer: The number of reactant species that collide in that step. Counts molecules/atoms participating in the elementary step.

Flashcard 23: What are the only possible molecularities for an elementary step in AP Chemistry?

Answer: Unimolecular, bimolecular, or termolecular. 1, 2, or 3 molecules colliding; higher is too improbable.

Flashcard 24: What is the rate law for a unimolecular elementary step A→A \rightarrowA→ products?

Answer: rate=k[A]\text{rate}=k[A]rate=k[A]. One molecule decomposes, so rate depends on [A] only.

Flashcard 25: What is the rate law for a bimolecular elementary step A+B→A+B \rightarrowA+B→ products?

Answer: rate=k[A][B]\text{rate}=k[A][B]rate=k[A][B]. Two different molecules collide, each contributes to rate.

Flashcard 26: What is the rate law for a bimolecular elementary step 2A→2A \rightarrow2A→ products?

Answer: rate=k[A]2\text{rate}=k[A]^2rate=k[A]2. Two A molecules collide, so [A] appears squared.

Flashcard 27: What is the rate law for a termolecular elementary step A+B+C→A+B+C \rightarrowA+B+C→ products?

Answer: rate=k[A][B][C]\text{rate}=k[A][B][C]rate=k[A][B][C]. Three molecules must collide simultaneously.

Flashcard 28: What is the rate law for a termolecular elementary step 2A+B→2A+B \rightarrow2A+B→ products?

Answer: rate=k[A]2[B]\text{rate}=k[A]^2[B]rate=k[A]2[B]. Two A's and one B collide; A contributes squared term.

Flashcard 29: What is the key rule linking stoichiometric coefficients to rate-law exponents for an elementary step?

Answer: For an elementary step, exponents equal reactant coefficients. Unlike overall reactions, elementary steps follow this rule.

Flashcard 30: Which option is correct: Can the overall reaction stoichiometry be used to write the overall rate law?

Answer: No; only an elementary step directly determines its rate law. Overall rate laws must be determined experimentally.