Core Concept
- Chemical equilibrium occurs when forward and reverse reaction rates are equal
- Concentrations of reactants and products remain constant (not necessarily equal)
- Denoted by in chemical equations
Equilibrium Constant ()
For a general reaction:
The equilibrium constant is:
- : Products are favored
- : Reactants are favored
- : Neither is strongly favored
Types of Equilibrium Constants
- : Based on concentrations (mol/L)
- : Based on partial pressures (atm)
- Relationship:
- Where moles of gaseous products - moles of gaseous reactants
Le Châtelier’s Principle
System at equilibrium will shift to counteract any imposed change:
-
Concentration changes:
- Adding reactant: Shifts right
- Adding product: Shifts left
- Removing reactant: Shifts left
- Removing product: Shifts right
-
Pressure/Volume changes (gases only):
- Increasing pressure: Shifts toward fewer gas molecules
- Decreasing pressure: Shifts toward more gas molecules
-
Temperature changes:
- Endothermic reaction ():
- Increasing temperature shifts right
- Decreasing temperature shifts left
- Exothermic reaction ():
- Increasing temperature shifts left
- Decreasing temperature shifts right
- Endothermic reaction ():
-
Catalysts:
- No effect on equilibrium position
- Only speeds up rate of reaching equilibrium
Calculating Equilibrium Concentrations
- Write balanced equation
- Set up ICE table (Initial, Change, Equilibrium)
- Express in terms of equilibrium concentrations
- Solve for unknown values
Reaction Quotient ()
- Same form as but uses non-equilibrium concentrations
- Comparing and :
- : Reaction shifts right
- : Reaction shifts left
- : System at equilibrium
Common Ion Effect
- Adding an ion already in solution shifts equilibrium
- Example: Adding to shifts left
Acid-Base Equilibrium
- : Acid dissociation constant
- : Base dissociation constant
- Relationship: at 25°C
Solubility
value /ksp >>> 1000 ⇒ approx rule todo (u can ignore x with this )
x from the ICE tables also represents solubility of a compound