Dynamic Chemical Equilibrium

• Dynamic chemical equilibrium is a state where the rate of the forward reaction equals the rate of the reverse reaction
• At equilibrium, the concentrations of reactants and products remain constant

Characteristics of Chemical Equilibrium

• Equilibrium is dynamic; forward and reverse reactions occur simultaneously
• Equilibrium is reached in a closed system; no matter can enter or leave
• Macroscopic properties are constant during equilibrium, such as concentration and pressure
• Equilibrium can be approached from either direction, using reactants or products
• Changing conditions like temperature, pressure, or concentration affects equilibrium

Equilibrium Constant (K)

• The equilibrium constant (K) is the ratio of product concentrations to reactant concentrations at equilibrium
• Each concentration is raised to the power of its stoichiometric coefficient
• For a reversible reaction aA + bB ⇌ cC + dD, the equilibrium constant expression is: K = ([C]^c[D]^d) / ([A]^a[B]^b)

Types of Equilibrium Constants

• K_c represents the equilibrium constant in terms of molar concentrations
• K_p indicates the equilibrium constant in terms of partial pressures (for gaseous reactions)
• K_p = K_c(RT)^Δn illustrates the relationship between K_c and K_p
  • Δn represents the change in the number of moles of gas (products - reactants)
  • R is the ideal gas constant
  • T is the temperature in Kelvin

Magnitude of K

• K > 1 means products are favored at equilibrium
• K < 1 means reactants are favored at equilibrium
• K ≈ 1 indicates that neither reactants nor products are strongly favored

Reaction Quotient (Q)

• The reaction quotient (Q) measures the relative amounts of products and reactants present in a reaction at any given time
• Q uses the same expression as K, but with initial or non-equilibrium concentrations
• If Q < K, the ratio of products to reactants is less than at equilibrium, therefore, the forward reaction is favored
• If Q > K, the ratio of products to reactants is greater than at equilibrium, therefore, the reverse reaction is favored
• If Q = K, the reaction is at equilibrium

Le Chatelier's Principle

• Le Chatelier's Principle describes how a system at equilibrium responds to counteract changes and establish a new equilibrium
• Changes include adding heat, altering reactant or product concentrations, or modifying pressure

Effect of Concentration

• Adding reactants shifts the equilibrium towards the products
• Adding products shifts the equilibrium towards the reactants
• Removing reactants shifts the equilibrium towards the reactants
• Removing products shifts the equilibrium towards the products

Effect of Pressure/Volume

• Increasing pressure (decreasing volume) shifts the equilibrium towards the side with fewer moles of gas
• Decreasing pressure (increasing volume) shifts the equilibrium towards the side with more moles of gas
• Pressure changes have negligible effect if no change occurs in the number of moles of gas

Effect of Temperature

• Increasing temperature shifts the equilibrium in the direction of the endothermic reaction (ΔH > 0)
• Decreasing temperature shifts the equilibrium in the direction of the exothermic reaction (ΔH < 0)
• Temperature changes affect the value of the equilibrium constant, K

Effect of Inert Gases

• Adding an inert gas at constant volume does not affect the equilibrium position
• Adding an inert gas at constant pressure shifts the equilibrium towards the side with more moles of gas

Effect of a Catalyst

• A catalyst speeds up both the forward and reverse reactions equally, thus not affecting the equilibrium position
• A catalyst affects only the rate at which equilibrium is reached

Dynamic chemical equilibrium is when the forward and reverse reaction rates are equal. Achieved in closed systems, it maintains constant macroscopic properties. Equilibrium constant (K) relates product to reactant concentrations at equilibrium, vital for predicting reaction direction.