Unit 5 AP chemistry Study Guide

AP Chemistry Unit 5: Kinetics

✨ Overview

This unit covers the study of chemical kinetics: how fast chemical reactions occur and the mechanisms by which they happen. Kinetics helps explain real-world processes like food preservation, catalytic converters, and laboratory rate determinations.

• Why cold temperatures slow food spoilage
• How catalytic converters work
• How rate laws are determined in labs

⚖️ Major Topics

5.1 Reaction Rates

• Rate = −Δ[Reactant]/Δt = Δ[Product]/Δt
• Units: mol·L⁻¹·s⁻¹
• Relative rate expressions based on coefficients

5.2 Introduction to Rate Laws

• Rate = k[A]ⁿ[B]^m (determined experimentally)
• Orders (n, m) are not from the coefficients unless it's an elementary step

5.3 Concentration vs. Time

First Order

Graph: ln[A] vs. t | Half-life = 0.693 / k

Second Order

Graph: 1/[A] vs. t | Half-life = 1 / (k[A]₀)

Zero Order

Graph: [A] vs. t | Half-life = [A]₀ / 2k

5.4 Elementary Reactions & Mechanisms

• Steps that sum to the overall reaction
• Slowest step = rate-determining step

5.5 Collision Model

• Effective collisions require proper orientation and sufficient energy

5.6 Energy Profile

• Activation Energy (Ea): energy barrier
• ΔH = Products - Reactants

5.7 - 5.10 Mechanisms & Energy Profiles

• Multistep reactions show multiple energy peaks
• Highest peak = rate-determining
• Pre-equilibrium method for intermediate substitution

5.11 Catalysis

• Lowers Ea, not consumed, does not affect ΔH

🔄 Practice Applications

• Determine rate law from data
• Use graphs to identify order
• Validate mechanisms against rate laws
• Sketch and interpret energy diagrams

📉 Common Misconceptions

• Reaction order = coefficients → ❌
• All collisions = reactions → ❌
• Catalysts change ΔH → ❌

📚 Review Summary

Order	Integrated Rate Law	Graph	Half-Life Formula
Zero	[A] = −kt + [A]₀	[A] vs. t	[A]₀ / 2k
First	ln[A] = −kt + ln[A]₀	ln[A] vs. t	0.693 / k
Second	1/[A] = kt + 1/[A]₀	1/[A] vs. t	1 / (k[A]₀)

🧬 Flashcard Points

• Rate = −Δ[Reactant]/Δt
• Rate Law = k[A]^n[B]^m
• 1st Order = ln[A] vs. t
• 2nd Order = 1/[A] vs. t
• 0 Order = [A] vs. t
• Catalyst = Lowers Ea, not used up
• Rate-Determining = Slowest Step
• Intermediates = Appear then disappear