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Le Chateliers Principle

Acids and Bases

Reaction Quotient

ICE Tables

Le Chateliers Principle

Base Dissociation Constant

Salt Hydrolysis

Solubility Product Constant

Key Concepts:

• Dynamic Equilibrium: A state where the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations of reactants and products. $ Rate_{forward} = Rate_{reverse} $

• Equilibrium Constant ( $ K $ ): A quantitative measure of the relative amounts of reactants and products at equilibrium. For the generic reaction: $ aA + bB \rightleftharpoons cC + dD $ , the equilibrium constant expression is:

$$ K = \frac{[C]]^c[D]]^d}{[A]]^a[B]]^b} $$

• ** $ K_c $ vs $ K_p $ **: $ K_c $ uses molar concentrations, while $ K_p $ uses partial pressures (for gaseous reactions). The relationship between them is given by:

$$ K_p = K_c(RT)^{\Delta n} $$

where $ \Delta n $ is the change in the number of moles of gas (moles of gaseous products - moles of gaseous reactants), $ R $ is the ideal gas constant, and $ T $ is the temperature in Kelvin.

• Reaction Quotient ( $ Q $ ): Similar to $ K $ , but uses concentrations at any point in the reaction, not just at equilibrium. Comparing $ Q $ to $ K $ predicts the direction the reaction will shift to reach equilibrium:

  • $ Q < K $ : Reaction shifts right (towards products)
  • $ Q > K $ : Reaction shifts left (towards reactants)
  • $ Q = K $ : Reaction is at equilibrium

• Le Chateliers Principle: If a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. Stresses include:

  • Changes in concentration: Adding reactant shifts right, adding product shifts left.
  • Changes in pressure/volume: Increasing pressure (decreasing volume) favors the side with fewer moles of gas. Decreasing pressure (increasing volume) favors the side with more moles of gas.
  • Changes in temperature:
    • Exothermic reactions ( $ \Delta H < 0 $ ): Increasing temperature shifts left, decreasing temperature shifts right.
    • Endothermic reactions ( $ \Delta H > 0 $ ): Increasing temperature shifts right, decreasing temperature shifts left.

• **Calculating Equilibrium Concentrations: Often involves setting up an ICE (Initial, Change, Equilibrium]]) table and solving for unknown concentrations using the equilibrium constant expression.

Equilibrium Calculations

Le Chateliers Principle Examples

Acid-Base Equilibria (This will cover weak acids/bases, $ K_a $ , $ K_b $ , pH calculations, buffers, etc.)

Solubility Equilibria (This will cover $ K_{sp} $ , solubility, common ion effect, etc.)