Equilibria

• What is a reversible reaction?

  A reaction where reactants form products that can reform the original reactants
• How is a reversible reaction represented?

  Using a double arrow

  
• What characterizes dynamic equilibrium in a reversible reaction?

  The forward and backward rates of reaction are the same
• What is required for dynamic equilibrium to occur?

  A closed system where no substances can enter or leave
• What does Le Chatelier’s Principle predict?

  How an equilibrium mixture will change if reaction conditions are altered
• What happens to a system when it is subject to change according to Le Chatelier’s Principle?

  The system will alter to lessen the effect of that change
• How can reaction conditions be altered to maximize yield in industry?

  By applying Le Chatelier’s Principle
• What effect does increasing temperature have on an endothermic reaction?

  It favors the endothermic reaction and increases the yield of endothermic products
• What happens when temperature is decreased in an exothermic reaction?

  It favors the exothermic reaction and increases the yield of exothermic products
• What is the significance of ∆H in exam questions regarding reactions?

  It indicates which direction is endothermic and which is exothermic

  
• How does increasing pressure affect a reversible reaction?

  It favors the side with fewer moles
• What is the effect of decreasing pressure on a reversible reaction?

  It favors the side with more moles
• What happens when the concentration of reactants is increased?

  It favors the reaction that produces the products
• What is the effect of decreasing the concentration of products?

  It favors the reaction that reforms the reactants
• How do catalysts affect the equilibrium position?


  Catalysts do not affect the equilibrium position
• What is the role of catalysts in reaching equilibrium?


  Catalysts allow equilibrium to be reached faster
• What does the equilibrium constant \( K_c \) indicate?

  The position of equilibrium for a reaction at a certain temperature

  
• When does the value of \( K_c \) change?

  When the reaction conditions and position of equilibrium are changed
• How is \( K_c \) calculated?

  By dividing the concentration of products by the concentration of reactants
• What happens to the moles in the \( K_c \) expression?

  Each substance is raised to a power equal to the number of moles
• How do the units of \( K_c \) vary?

  The units depend on the specific chemical reaction
• What factors affect the value of \( K_c \)?

  It is affected by changing the reaction temperature
• What does changing the concentration of reactants do to \( K_c \)?


  It does not affect the value of \( K_c \)
• How does the addition of a catalyst influence \( K_c \)?


  It does not affect the value of \( K_c \)
• What are the key concepts of Le Chatelier’s Principle?

  • Predicts changes in equilibrium when conditions are altered
  • System alters to lessen the effect of the change
  • Useful in maximizing yield in industrial processes
• What are the effects of changing temperature, pressure, and concentration on equilibrium?

  • **Temperature**:
  • Increasing favors endothermic reactions
  • Decreasing favors exothermic reactions
  • **Pressure**:
  • Increasing favors side with fewer moles
  • Decreasing favors side with more moles
  • **Concentration**:
  • Increasing reactants favors products
  • Decreasing products favors reactants
• What is the significance of the equilibrium constant \( K_c \)?

  • Indicates position of equilibrium at a certain temperature
  • Remains constant unless reaction conditions change
  • Calculated from concentrations of products and reactants

  
• What factors do not affect the value of \( K_c \)?

  • Concentration changes
  • Addition of catalysts