Overview
This lecture explains reversible reactions, chemical equilibrium, and how the position of equilibrium can shift depending on conditions.
Reversible Reactions
- A reversible reaction is shown with a double arrow, indicating products can reform reactants.
- Example: Ammonium chloride ⇄ ammonia + hydrogen chloride.
Equilibrium
- At equilibrium, the rate of the forward and backward reactions are equal.
- Concentrations of reactants and products remain constant at equilibrium but are not necessarily equal.
- Equilibrium can only occur in a closed system where no reactants or products escape.
Position of Equilibrium
- The position of equilibrium refers to the relative concentrations of reactants and products.
- If there are more products, equilibrium "lies to the right"; more reactants mean it "lies to the left."
- Changing conditions (like temperature) can shift equilibrium to favor more reactants or products.
Effect of Temperature and Energy Changes
- Reversible reactions are exothermic (release energy) in one direction and endothermic (absorb energy) in the other.
- Example: Thermal decomposition of hydrated copper sulfate is endothermic; the reverse reaction (rehydration) is exothermic.
- Adding heat favors the endothermic direction; cooling favors the exothermic direction.
Key Terms & Definitions
- Reversible reaction — a reaction that can go in both the forward and backward directions.
- Equilibrium — the state where the rates of forward and backward reactions are equal, and concentrations remain constant.
- Position of equilibrium — indicates whether more reactants or more products are present at equilibrium.
- Closed system — a sealed environment where no substances can enter or leave.
- Exothermic — a reaction that releases energy to the surroundings.
- Endothermic — a reaction that absorbs energy from the surroundings.
- Hydrated — a substance containing water.
- Anhydrous — a substance with no water present.
Action Items / Next Steps
- Review examples of reversible reactions and practice identifying forward and backward directions.
- Understand the effect of temperature on the position of equilibrium.
- Prepare for next class by reading about Le Chatelier's principle.