Kinetics
Caleb Thomas
10 min read
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Study Guide Overview
This study guide covers kinetics, the study of reaction rates, including: reaction rates, rate laws, concentration changes over time, elementary reactions, the collision model, reaction energy profiles, reaction mechanisms, the steady-state approximation, multistep reaction energy profiles, and catalysis. Key concepts include rate constants, reaction orders, half-life, activation energy, and the rate-determining step. Practice questions and exam tips are also provided.
#AP Chemistry Unit 5: Kinetics - The Ultimate Study Guide 🚀
Welcome to your go-to guide for AP Chemistry Unit 5! This unit focuses on kinetics, the study of reaction rates. Let's break it down and get you ready for the exam. Remember, about 7-9% of the exam will cover this material, so it's crucial to master these concepts. ✍️
#What is Kinetics?
Kinetics is all about how fast chemical reactions occur. It's not just about whether a reaction can happen, but how quickly it proceeds. Think of it like knowing if a car can move versus knowing how fast it's moving.
# 5.1 Reaction Rates
#What is Reaction Rate?
The rate of a reaction is the speed at which reactants are converted into products. We measure this by tracking the change in concentration of reactants or products over time.
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Rate = -Δ[Reactant]/t (negative sign indicates reactant is decreasing)
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Rate = Δ[Product]/t
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Units: mol/L·s or M/s (Molarity per second)
Pay close attention to the units! They can change (e.g., hours instead of seconds). Always double-check your units in calculations.
#Visualizing Reaction Rate
The rate of a reaction can be visualized as the slope of a concentration vs. time graph.
- The steeper the slope, the faster the reaction.
- Reactant concentration decreases over time (negative slope).
- Product concentration increases over time (positive slope).
# 5.2 Introduction to Rate Law
#What is a Rate Law?
A rate law is an equation that shows how the rate of a reaction depends on the concentrations of reactants. It's determined experimentally.
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General form: Rate = k[A]ⁿ[B]ᵐ...
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R is the rate of the reaction
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k is the rate constant (temperature-specific!)
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[A] and [B] are reactant concentrations
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n and m are reaction orders (not from stoichiometry!)
Don't use stoichiometric coefficients to determine reaction orders! Reaction orders must be found experimentally.
#Reaction Orders
Reaction order describes how the rate changes when reactant concentrations change. For example:
- Zero order: Changing reactant concentration has no effect on the rate.
- First order: Doubling reactant concentration doubles the rate.
- Second order: Doubling reactant concentration quadruples the rate.
#Rate Constant (k)
The rate constant (k) is a proportionality constant specific to each reaction at a given temperature.
- It indicates how fast a reaction proceeds at a specific temperature.
- k is temperature-dependent; it increases with temperature.
# 5.3 Concentration Changes Over Time
#Differential vs. Integrated Rate Laws
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Differential rate law (what we just discussed) shows how rate changes with concentration.
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Integrated rate law shows how concentration changes with time. (This is what we'll focus on here)
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