net reaction moves toward products
⚖️AP CHEMISTRY STUDY GUIDE
Unit 7: Equilibrium
Study reversible reactions, equilibrium constants, reaction quotients, concentration effects, pressure effects, and solubility for AP Chemistry Unit 7.
8 key ideas8 flashcards5 practice questions
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One comparison predicts the net direction.
forward rate equals reverse rate
net reaction moves toward reactants
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
At equilibrium, forward and reverse reaction rates are equal.
- 02
Equilibrium concentrations remain constant over time but need not be equal.
- 03
An equilibrium constant relates product and reactant activities at a fixed temperature.
- 04
Pure solids and pure liquids are omitted from heterogeneous equilibrium expressions.
- 05
The reaction quotient has the same form as the equilibrium expression but can describe any point in time.
- 06
Comparing the reaction quotient with the equilibrium constant predicts the net reaction direction.
- 07
A system responds to an altered concentration, pressure, or temperature by reaching another equilibrium state.
- 08
A catalyst speeds both directions and does not alter the equilibrium composition.
PART OF THE AP CHEMISTRY GUIDE
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Open the full AP Chemistry guide →Two ideas worth correcting now
NOT QUITE
→Equilibrium means the reaction has stopped
USE THIS INSTEAD
Forward and reverse reactions continue at equal rates.
NOT QUITE
→A catalyst pushes equilibrium toward products
USE THIS INSTEAD
It speeds forward and reverse reactions without altering equilibrium composition.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What is true of forward and reverse rates at equilibrium?Show answer ＋
They are equal.
2Are reactant and product concentrations equal at equilibrium?Show answer ＋
Not necessarily. They are constant but may differ.
3What does a large equilibrium constant indicate?Show answer ＋
Products predominate at equilibrium under the stated temperature.
4Which substances are omitted from a heterogeneous equilibrium expression?Show answer ＋
Pure solids and pure liquids.
5What happens when Q is less than K?Show answer ＋
The net reaction proceeds toward products until equilibrium is reached.
6What happens when Q is greater than K?Show answer ＋
The net reaction proceeds toward reactants until equilibrium is reached.
7What alters an equilibrium constant?Show answer ＋
Temperature.
8What does a catalyst do to equilibrium attainment?Show answer ＋
It reduces the time needed to reach equilibrium without altering equilibrium composition.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01Why can a reaction continue in both directions at equilibrium without a concentration trend?
Forward and reverse reactions occur at equal rates, so their concentration effects cancel.
02How does adding a reactant affect Q immediately?
The larger reactant term makes Q smaller for a reaction written with that reactant in the denominator.
03Why does compressing a gas mixture favor the side with fewer gas particles?
The system can reduce pressure by consuming gas particles when the reaction stoichiometry permits it.
04How can K for a reversed reaction be obtained?
Take the reciprocal of the original equilibrium constant.
05Why does a catalyst leave K unchanged?
It affects activation barriers rather than the thermodynamic relation between reactants and products.
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