⚗️ AP® Chemistry
📊
Unit 5: Kinetics
Complete Collection
2017 • 2018 • 2019 • 2022 • 2023 • 2024
Free-Response Questions with Full Solutions
📚 COMPREHENSIVE COVERAGE
⚛️
✓ Rate Laws & Reaction Orders
✓ Integrated Rate Laws
✓ Collision Theory & Activation Energy
✓ Reaction Mechanisms & RDS
✓ Temperature Effects on Rates
Mr. Hisham Mahmoud
Professional Chemistry Educator
🧪
AP C H E MIS T RYRE S CUE .CO M
\"From 'I Don't Get It' to 'I Ace It'\"
AP® is a registered trademark of the College Board
,AP® Chemistry Kinetics Questions (Unit
5)
2017-2024 Exams - Complete Solutions with Explanations
Prepared by Mr. Hisham Mahmoud | APChemistryRescue.com
📋 Document Overview
2017 Exam: Question 1(b) - Temperature effects on collision energy and
activation energy
2018 Exam: Question (e), (f) - First-order kinetics, rate constant calculation,
experimental design
2019 Exam: Question 6(a), (b), (c) - Second-order kinetics, rate law, and
mechanisms
2022 Exam: Question 5(a), (b), (c) - Rate constant, mechanism, and rate-
determining step
2023 Exam: Question 3(b), (c), (d) - Factors affecting reaction rate
2024 Exam: Question 2(b) - Surface area effects; Question 6 - Second-order
kinetics
2017 AP® Chemistry Exam
Question 1(b) - Temperature Effects on Collision Energy and Activation
Energy
Reaction Context:
CS2(g) + 3 Cl2(g) → CCl4(g) + S2Cl2(g)
Carbon tetrachloride, CCl4(g), can be synthesized according to the reaction
above. A chemist runs the reaction at a constant temperature of 120°C in a
rigid 25.0 L container.
,At 30°C the reaction is thermodynamically favorable, but no reaction is
observed to occur. However, at 120°C, the reaction occurs at an observable
rate.
1(b)(i): Explain how the higher temperature affects the collisions
between the reactant molecules so that the reaction occurs at an
observable rate at 120°C.
Answer:
At higher temperature (120°C), the reactant molecules have greater average
kinetic energy, which means they move faster and collide with greater
energy. More collisions have energy equal to or greater than the activation
energy (Ea), resulting in a greater fraction of effective collisions that can
overcome the activation barrier and produce products.
Explanation:
Temperature-Kinetic Energy Relationship:
At 30°C: Molecules have lower average kinetic energy
At 120°C: Molecules have higher average kinetic energy
KEavg = (3/2)RT (directly proportional to temperature)
Effect on Collisions:
Higher velocity: Molecules move faster, increasing collision frequency
More energetic collisions: Each collision carries more kinetic energy
Greater fraction above Ea: More molecules have sufficient energy to
react
Activation Energy Concept:
For a reaction to occur, colliding molecules must have energy ≥ E
a
(activation energy). At 30°C, very few collisions meet this requirement. At
, 120°C, a significantly larger fraction of collisions have E ≥ Ea, making the
reaction observable.
Arrhenius Equation Connection:
-Ea/RT
k = Ae
As temperature (T) increases, the exponential term becomes less negative,
making k (rate constant) larger, and thus the reaction rate increases
exponentially.
Mr. Hisham's Note: Think of molecules like billiard balls on a pool table.
At low temperature, they're rolling slowly - when they bump into each other,
nothing much happens. At high temperature, they're zooming around like
race cars - when they collide, BAM!💥 Enough energy to break bonds and
make new ones. That's why we heat things up in chemistry! 🔥
1(b)(ii): The graph below shows a distribution for the collision energies
of reactant molecules at 120°C. Draw a second curve on the graph that
shows the distribution for the collision energies of reactant molecules
at 30°C.
Answer:
Characteristics of the 30°C curve:
Peak height: HIGHER than the 120°C curve
Peak position: Shifted to the LEFT (lower energy)
Curve width: NARROWER distribution
Area under curve: Same as 120°C curve (same total number of
molecules)
Area beyond Ea: MUCH SMALLER (fewer molecules with sufficient
energy to react)
📊
Unit 5: Kinetics
Complete Collection
2017 • 2018 • 2019 • 2022 • 2023 • 2024
Free-Response Questions with Full Solutions
📚 COMPREHENSIVE COVERAGE
⚛️
✓ Rate Laws & Reaction Orders
✓ Integrated Rate Laws
✓ Collision Theory & Activation Energy
✓ Reaction Mechanisms & RDS
✓ Temperature Effects on Rates
Mr. Hisham Mahmoud
Professional Chemistry Educator
🧪
AP C H E MIS T RYRE S CUE .CO M
\"From 'I Don't Get It' to 'I Ace It'\"
AP® is a registered trademark of the College Board
,AP® Chemistry Kinetics Questions (Unit
5)
2017-2024 Exams - Complete Solutions with Explanations
Prepared by Mr. Hisham Mahmoud | APChemistryRescue.com
📋 Document Overview
2017 Exam: Question 1(b) - Temperature effects on collision energy and
activation energy
2018 Exam: Question (e), (f) - First-order kinetics, rate constant calculation,
experimental design
2019 Exam: Question 6(a), (b), (c) - Second-order kinetics, rate law, and
mechanisms
2022 Exam: Question 5(a), (b), (c) - Rate constant, mechanism, and rate-
determining step
2023 Exam: Question 3(b), (c), (d) - Factors affecting reaction rate
2024 Exam: Question 2(b) - Surface area effects; Question 6 - Second-order
kinetics
2017 AP® Chemistry Exam
Question 1(b) - Temperature Effects on Collision Energy and Activation
Energy
Reaction Context:
CS2(g) + 3 Cl2(g) → CCl4(g) + S2Cl2(g)
Carbon tetrachloride, CCl4(g), can be synthesized according to the reaction
above. A chemist runs the reaction at a constant temperature of 120°C in a
rigid 25.0 L container.
,At 30°C the reaction is thermodynamically favorable, but no reaction is
observed to occur. However, at 120°C, the reaction occurs at an observable
rate.
1(b)(i): Explain how the higher temperature affects the collisions
between the reactant molecules so that the reaction occurs at an
observable rate at 120°C.
Answer:
At higher temperature (120°C), the reactant molecules have greater average
kinetic energy, which means they move faster and collide with greater
energy. More collisions have energy equal to or greater than the activation
energy (Ea), resulting in a greater fraction of effective collisions that can
overcome the activation barrier and produce products.
Explanation:
Temperature-Kinetic Energy Relationship:
At 30°C: Molecules have lower average kinetic energy
At 120°C: Molecules have higher average kinetic energy
KEavg = (3/2)RT (directly proportional to temperature)
Effect on Collisions:
Higher velocity: Molecules move faster, increasing collision frequency
More energetic collisions: Each collision carries more kinetic energy
Greater fraction above Ea: More molecules have sufficient energy to
react
Activation Energy Concept:
For a reaction to occur, colliding molecules must have energy ≥ E
a
(activation energy). At 30°C, very few collisions meet this requirement. At
, 120°C, a significantly larger fraction of collisions have E ≥ Ea, making the
reaction observable.
Arrhenius Equation Connection:
-Ea/RT
k = Ae
As temperature (T) increases, the exponential term becomes less negative,
making k (rate constant) larger, and thus the reaction rate increases
exponentially.
Mr. Hisham's Note: Think of molecules like billiard balls on a pool table.
At low temperature, they're rolling slowly - when they bump into each other,
nothing much happens. At high temperature, they're zooming around like
race cars - when they collide, BAM!💥 Enough energy to break bonds and
make new ones. That's why we heat things up in chemistry! 🔥
1(b)(ii): The graph below shows a distribution for the collision energies
of reactant molecules at 120°C. Draw a second curve on the graph that
shows the distribution for the collision energies of reactant molecules
at 30°C.
Answer:
Characteristics of the 30°C curve:
Peak height: HIGHER than the 120°C curve
Peak position: Shifted to the LEFT (lower energy)
Curve width: NARROWER distribution
Area under curve: Same as 120°C curve (same total number of
molecules)
Area beyond Ea: MUCH SMALLER (fewer molecules with sufficient
energy to react)
