Chemistry Chapter: Equilibrium and Le Chatelier's Principle

Equilibrium

• Equilibrium is a state where the rates of the forward and reverse reactions are equal.
• At equilibrium, the net change in concentrations of reactants and products is zero. This does not mean that the forward and reverse processes have stopped, rather that the rate of each process is equal.

Le Chatelier's Principle

• Le Chatelier's Principle states that if a stress is applied to a system in equilibrium, the system shifts in a direction that relieves the stress.
• The stress can involve changes in concentration, pressure, temperature, or the addition of a catalyst.
• Increasing the concentration of a reactant shifts the equilibrium to the right (favoring product formation).
• Decreasing the concentration of a product has the same effect.
• Increasing the pressure on a gaseous system shifts the equilibrium to the side with fewer moles of gas.
• Increasing the temperature shifts the equilibrium in the direction that absorbs heat (endothermic reaction).
• Adding a catalyst speeds up both the forward and reverse reactions, but does not affect the position of equilibrium.

Equilibrium Constants

• Equilibrium constants (often denoted by K) quantify the relative amounts of products and reactants at equilibrium.
• The numerical value of K depends on the specific reaction and the temperature.
• For the general reversible reaction aA + bB ⇌ cC + dD, the equilibrium constant is defined as: K = ([C]^c * [D]^d) / ([A]^a * [B]^b), where the square brackets denote molar concentrations.
• Large K values mean that the reaction strongly favors product formation.
• Small K values mean that the reaction strongly favors reactant formation.

Factors Affecting Equilibrium

• Concentration Changes: Adding more reactants or removing products drives the reaction towards products. Removing reactants or adding products shifts the reaction towards reactants.
• Pressure Changes (for gaseous reactions): Increasing the pressure shifts the reaction towards the side with fewer moles of gas. Decreasing the pressure shifts the reaction towards the side with more moles of gas.
• Temperature Changes: Increasing the temperature shifts the equilibrium in favor of the endothermic reaction (the reaction that absorbs heat). Decreasing the temperature shifts the equilibrium in favor of the exothermic reaction (the reaction that releases heat).
• Catalysts: Catalysts speed up both the forward and reverse reactions equally, without changing the position of equilibrium.

Dynamic Equilibrium

• Dynamic equilibrium is the state where the forward and reverse reactions occur at equal rates.
• The concentrations of reactants and products remain constant over time because the rate of the forward reaction equals the rate of the reverse reaction.

Ionic Equilibrium

• Ionic equilibrium deals with the equilibrium between ions and undissociated molecules in solution.
• Examples include the dissociation of weak acids and bases, and the precipitation of sparingly soluble salts.
• The equilibrium constant for such reactions describes the extent of ionization or solubility.
• Common ion effect: The solubility of a slightly soluble salt is decreased when a soluble salt containing a common ion is added to the solution.
• Buffer solutions resist changes in pH. They typically contain a weak acid and its conjugate base, or a weak base and its conjugate acid.

This quiz explores the concepts of equilibrium and Le Chatelier's Principle in chemistry. Students will learn how changes in concentration, pressure, and temperature affect a system at equilibrium. Test your knowledge on the principles governing chemical reactions and equilibrium states.