College Board-Aligned Original Notes
AP Chemistry 5.2: Introduction to rate law
Relate reaction rate to reactant concentrations using experimental data.
Aligned to Kinetics from the current College Board AP Chemistry course outline. Exam weighting for this unit: 7%-9% of the multiple-choice score range listed by College Board.
What To Know
- Rate laws are determined experimentally.
- Reaction orders show how rate depends on concentration.
- The overall reaction order is the sum of exponents in the rate law.
Detailed Notes
Introduction to rate law is part of Unit 5: Kinetics. The main skill is to relate reaction rate to reactant concentrations using experimental data. Before answering, decide whether the prompt is asking for a particulate explanation, a mathematical setup, a graph interpretation, or a connection between more than one representation.
The first idea to keep straight is that rate laws are determined experimentally. In the same topic, remember that reaction orders show how rate depends on concentration. A complete AP answer also uses the fact that the overall reaction order is the sum of exponents in the rate law. These ideas should be tied to specific particles, charges, attractions, energy changes, or measured quantities rather than stated as isolated facts.
For calculations or symbolic work, anchor the solution with rate = k[A]^m[B]^n. Define what each quantity represents, substitute values with units, and check whether the sign, magnitude, charge balance, atom balance, or equilibrium direction makes chemical sense for this topic.
If doubling [A] doubles rate, the reaction is first order in A. In a free-response explanation, state the chemistry concept first, show the relevant equation or representation, and then explain how the evidence supports the conclusion for introduction to rate law.
Key Vocabulary
Rate law
An experimentally determined equation relating rate to reactant concentrations.
Rate constant
The proportionality constant in a rate law at a fixed temperature.
Reaction order
An exponent in a rate law showing how concentration affects rate.
Overall order
The sum of the concentration exponents in a rate law.
Useful Relationships
Worked Study Approach
If doubling [A] doubles rate, the reaction is first order in A.
Common Mistakes
- Using a memorized rule without explaining the chemical reason behind it.
- Forgetting to conserve atoms, charge, energy, or units when the topic involves calculations.
- Mixing up particle-level explanations with macroscopic observations.
Quick Practice
How would you explain Introduction to rate law in one sentence?
Use the focus statement above, then add one particle-level or mathematical detail.
What evidence would support an AP-style answer on this topic?
Use a balanced equation, diagram, graph, table, numerical setup, or particulate model depending on the prompt.