Overview
This lecture explains reversible reactions, equilibrium, the position of equilibrium, and how conditions affect these concepts in chemical systems.
Reversible Reactions
- Reversible reactions are indicated by a double arrow and can proceed in both forward and backward directions.
- The forward reaction forms products from reactants, while the backward reaction reforms reactants from products.
- Both reactions can occur at different rates initially, but may become equal over time.
Chemical Equilibrium
- Equilibrium is reached when the forward and backward reaction rates are equal.
- At equilibrium, concentrations of reactants and products remain constant even though both reactions continue.
- Equilibrium requires a closed system so that reactants and products cannot escape.
Position of Equilibrium
- The position of equilibrium refers to which side (reactants or products) is favored at equilibrium.
- If products are greater, equilibrium lies to the right; if reactants are greater, equilibrium lies to the left.
- Changing conditions, like temperature, can shift the position of equilibrium.
Effects of Temperature on Equilibrium
- Adding heat favors the endothermic reaction, shifting equilibrium to the side that absorbs heat (more products or more reactants).
- Cooling favors the exothermic reaction, shifting equilibrium in the opposite direction.
Exothermic and Endothermic Directions
- Every reversible reaction is exothermic in one direction and endothermic in the other.
- Example: The thermal decomposition of hydrated copper sulfate is endothermic forward (needs heat) and exothermic backward (releases heat).
Key Terms & Definitions
- Reversible reaction — a chemical reaction that can proceed in both forward and backward directions.
- Equilibrium — the state where forward and backward reaction rates are equal and concentrations are constant.
- Position of equilibrium — the relative amounts of reactants and products at equilibrium.
- Closed system — an environment where no substances can enter or leave the reaction.
- Exothermic reaction — a reaction that releases heat.
- Endothermic reaction — a reaction that absorbs heat.
- Hydrated — containing water molecules.
- Anhydrous — lacking water molecules.
Action Items / Next Steps
- Review definitions of equilibrium, exothermic, and endothermic reactions.
- Practice identifying the direction of shift in position of equilibrium with changes in conditions.