rate = r
⏱️AP CHEMISTRY STUDY GUIDE
Unit 5: Kinetics
Study reaction rates, rate laws, mechanisms, collision theory, energy profiles, and catalysts for AP Chemistry Unit 5.
8 key ideas8 flashcards5 practice questions
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Alter one concentration and compare the starting rate.
rate = 2ʸr
use the measured ratio
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
Reaction rate measures concentration shift per unit time.
- 02
A rate law relates reaction rate to reactant concentrations through experimentally determined exponents.
- 03
The rate constant depends on temperature and the reaction pathway.
- 04
An elementary step's molecularity determines its rate-law form.
- 05
A proposed mechanism must sum to the overall reaction and agree with the measured rate law.
- 06
Effective collisions require adequate energy and suitable orientation.
- 07
The Arrhenius equation relates the rate constant to temperature and activation energy.
- 08
A catalyst provides another pathway with lower activation energy without altering the equilibrium constant.
PART OF THE AP CHEMISTRY GUIDE
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Open the full AP Chemistry guide →Two ideas worth correcting now
NOT QUITE
→Reaction order comes directly from stoichiometric coefficients
USE THIS INSTEAD
Orders are measured experimentally unless the reaction is a stated elementary step.
NOT QUITE
→A catalyst makes an unfavorable reaction favorable
USE THIS INSTEAD
A catalyst affects rate, not the thermodynamic driving force or equilibrium constant.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What is a rate law?Show answer ＋
An equation relating reaction rate to reactant concentrations and a rate constant.
2How is reaction order determined?Show answer ＋
From experimental rate data, not from the overall balanced equation.
3What does the rate constant depend on?Show answer ＋
Temperature, pathway, and the identity of the reacting system.
4What is an elementary step?Show answer ＋
A single molecular event in a reaction mechanism.
5What is an intermediate?Show answer ＋
A species formed in one step and consumed in a later step.
6What is the rate-determining step?Show answer ＋
A slow step that limits the rate under the stated mechanism.
7What does activation energy represent?Show answer ＋
The energy barrier between reactants and the transition state.
8What does a catalyst do to activation energy?Show answer ＋
It supplies another pathway with a lower barrier.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01If doubling a reactant concentration quadruples the rate, what is its reaction order?
Second order with respect to that reactant because two raised to the second power equals four.
02Why can a balanced overall equation fail to predict the rate law?
The overall equation does not identify the sequence of elementary steps.
03How can a mechanism be tested against an experimental rate law?
Derive the rate expression from its slow step and any required fast equilibrium, then compare it with measured exponents.
04Why does higher temperature usually increase reaction rate?
A larger fraction of collisions has enough energy to cross the activation barrier.
05Why does a catalyst not alter the equilibrium constant?
It lowers barriers for forward and reverse pathways without altering their energy difference.
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