Overview
This lesson introduces chemical equilibrium, explaining how reversible reactions reach dynamic equilibrium and the conditions required for this process.
Types of Chemical Reactions
- Reactions with a single arrow proceed to completion, meaning reactants are used up and do not reform.
- In some reactions, products can revert back to reactants, making the reaction reversible.
- A reversible reaction is indicated by a double (⇌) or half-arrow symbol.
Dynamic Chemical Equilibrium
- Dynamic chemical equilibrium occurs when the forward and reverse reaction rates are equal.
- At equilibrium, reactants and products are continuously formed, but their concentrations remain constant.
- The reaction does not stop at equilibrium; both forward and reverse processes continue.
Forward and Reverse Reactions
- The forward reaction converts reactants into products.
- The reverse reaction converts products back into reactants.
- At the start, the forward reaction rate is high and the reverse rate is low, but they become equal at equilibrium.
Requirements for Equilibrium
- The system must be closed (no matter enters or leaves).
- The reaction must be reversible.
- Closed systems can be physical containers or conditions where no significant matter exchange occurs.
Examples of Equilibrium
- Phase change equilibrium: Water vaporizes and condenses at equal rates in a closed container.
- Graphs show that initially, the forward reaction rate is high and the reverse is zero, but they equalize over time.
Factors Affecting Equilibrium
- The position of equilibrium can be affected by temperature, concentration, or pressure (TCP).
- According to Le Chatelier's Principle, adding more reactant shifts equilibrium to oppose the change (e.g., favoring the forward reaction to reduce excess).
Upcoming Topics
- Further lessons will cover Le Chatelier’s Principle, equilibrium constant (Kc), and interpreting equilibrium graphs.
Key Terms & Definitions
- Chemical Equilibrium — State where forward and reverse reaction rates are equal.
- Reversible Reaction — A reaction where products can convert back to reactants.
- Closed System — A system isolated from its surroundings; no exchange of matter.
- Dynamic Equilibrium — Continuous reaction in both directions with constant concentrations.
- Le Chatelier’s Principle — When equilibrium is disturbed, the system shifts to oppose the change.
- Equilibrium Constant (Kc) — A value expressing the ratio of product to reactant concentrations at equilibrium.
Action Items / Next Steps
- Review the concepts of forward and reverse reactions.
- Prepare to study factors affecting equilibrium, Le Chatelier’s Principle, and Kc in upcoming lessons.