AP Chemistry — Unit 5: Kinetics
Practice questions, answers, and key terms for Unit 5, aligned to the College Board CED.
Exam weighting: Unit 5 is 7-9% of the AP Chemistry exam.
What AP Chemistry Unit 5 covers
The College Board Course and Exam Description breaks Unit 5 into 11 topics:
- 5.1 Reaction Rates
- 5.2 Introduction to Rate Law
- 5.3 Concentration Changes Over Time
- 5.4 Elementary Reactions
- 5.5 Collision Model
- 5.6 Reaction Energy Profile
- 5.7 Introduction to Reaction Mechanisms
- 5.8 Reaction Mechanism and Rate Law
- 5.9 Steady-State Approximation
- 5.10 Multistep Reaction Energy Profile
- 5.11 Catalysis
AP Chemistry Unit 5 practice questions
What does the reaction rate of a chemical reaction measure?
How fast reactant concentration changes over time. It's change in concentration over change in time.
For the reaction 4NH₃ + 5O₂ → 4NO + 6H₂O, how does the rate of disappearance of O₂ relate to the rate of appearance of H₂O?
O₂'s rate of disappearance × 6/5 equals H₂O's rate of appearance. Coefficients (5 and 6) set the ratio of rates.
A steel nail sits in acid for hours barely fizzing, but the same mass of steel wool reacts violently in seconds. Same metal, same amount — so why the huge rate difference?
Surface area — shredding the solid exposes more atoms to the acid. More exposed surface means more simultaneous collisions, so a faster rate.
What is a rate law, and what does each symbol in rate = k[A]^m[B]^n represent?
It relates rate to k and reactant concentrations raised to exponents m and n. Exponents m and n are found experimentally, not from coefficients.
What is the overall reaction order, and how is it determined from a rate law?
The sum of all the reactant exponents in the rate law. Each exponent is that reactant's order; together they give overall order.
What are the units of the rate constant k for a second-order reaction?
L·mol⁻¹·s⁻¹, equivalently M⁻¹s⁻¹ for second order. They yield M·s⁻¹ when multiplied by concentration squared.
In an initial rates experiment, doubling [A] quadruples the rate while [B] is held constant. What is the order with respect to A?
Second order with respect to A, because rate is proportional to [A]², and 2² = 4.
Which graphical plot produces a straight line for a zero-order reaction?
A plot of [A] versus time produces a straight line with slope equal to −k.
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Key terms in Unit 5
These 12 terms show up in the Unit 5 cards. Each one links to its definition in the AP Chemistry key-term reference.
Drill all of Unit 5 with spaced repetition
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