Chemical Equilibrium
Dynamic balance
Equilibrium concept
At equilibrium, forward and reverse reaction rates are equal, so concentrations remain constant even though molecules continue reacting. Equilibrium is dynamic, not static.
Equilibrium constant
For a reaction the equilibrium constant in concentration form is Pure solids and liquids are omitted because their activities are effectively constant.
Comparing Q and K
| Relationship | Meaning | Direction |
|---|---|---|
| Too many reactants | Shifts right | |
| At equilibrium | No net shift | |
| Too many products | Shifts left |
Le Châtelier's principle
If a system at equilibrium is disturbed, it shifts to partially oppose the disturbance.
If , the reaction will move
When the reaction quotient is smaller than , product formation is favored until equilibrium is restored.
Correct answer: Right
What does it mean when a system is at equilibrium?
The concentrations stay constant because the two reaction directions balance each other.
Correct answer: Forward and reverse rates are equal
Effects of disturbance
Add reactant
- System shifts toward products
- decreases relative to
Add product
- System shifts toward reactants
- increases relative to
Which expression correctly omits species in equilibrium calculations?
Pure solids and liquids are not included in equilibrium expressions because their activities are constant.
Correct answer: Solids and liquids