Overview
This lecture explains reversible reactions, the concept of dynamic equilibrium, and how equilibrium is established and maintained in chemical systems.
Reversible Reactions
- Many chemical reactions are reversible, meaning products can react to reform original reactants.
- Reversible reactions are represented by a double arrow (⇌).
- Both forward (reactants to products) and backward (products to reactants) processes occur.
Dynamic Equilibrium
- In a closed system, reversible reactions reach dynamic equilibrium where rates of forward and backward reactions are equal.
- Initially, forward reaction is fast due to abundant reactants.
- As products build up, backward reaction rate increases.
- Dynamic equilibrium means reactant and product concentrations stay constant but not necessarily equal.
- The reaction mixture appears unchanging despite ongoing reactions.
Conditions for Equilibrium
- A closed system (no entry or exit of substances) is required for equilibrium.
- Altering temperature, pressure, or other conditions disrupts equilibrium; the system will adjust to establish a new one.
Features of Reversible Reactions and Equilibrium
- Before equilibrium: concentrations and appearance change, reaction rates are unequal.
- At equilibrium: concentrations remain constant, reaction appears unchanging, reaction rates are equal.
- After changing conditions: system adjusts to a new equilibrium, rates and concentrations briefly change.
Position of Equilibrium
- Position of equilibrium shows the relative amounts of reactants and products at equilibrium.
- "Equilibrium lies to the right" means more products than reactants.
- "Equilibrium lies to the left" means more reactants than products.
Key Terms & Definitions
- Reversible Reaction — a chemical reaction where products can reform reactants.
- Closed System — a setup where no substances can enter or leave.
- Dynamic Equilibrium — state where forward and backward reaction rates are equal and concentrations remain constant.
- Position of Equilibrium — indicates whether products or reactants are favored at equilibrium.
Action Items / Next Steps
- Review examples of reversible reactions and identify the equilibrium position.
- Practice drawing and interpreting equilibrium graphs.