Chemical Equilibria

• In what type of systems does equilibrium occur?

  Only in closed systems
• What does Le Chatelier's principle state?

  If an external condition is changed the equilibrium shifts to counteract the change
• What happens to equilibrium if the concentration of a reactant is increased?

  Equilibrium shifts to the right
• What is the role of catalysts in equilibrium reactions?

  They speed up both forward and backward reactions
• What is the significance of the molar values in the KC expression?

  They become powers in the expression
• What is the KC expression for the reaction involving SO2, O2, and SO3?

  KC = [SO3]²/[SO2]²[O2]
• What do square brackets indicate in a KC expression?

  Concentration of reactants and products
• What is the unit for concentration used in KC calculations?

  Mol dm-³
• What happens to equilibrium with an increase in temperature?

  It shifts to favor the endothermic reaction
• What is the effect of decreasing temperature on equilibrium?

  It shifts to favor the exothermic reaction
• What happens with an increase in reactant concentration?

  Equilibrium shifts to favor product formation
• What occurs with a decrease in reactant concentration?

  Equilibrium shifts to favor reactant formation
• What happens with an increase in pressure?

  Equilibrium shifts to favor the side with fewer gaseous moles
• What occurs with a decrease in pressure?

  Equilibrium shifts to favor the side with more gaseous moles
• What is the compromise made in temperature for industrial reactions?

  High enough for fast rate, low for good yield
• What does the equilibrium constant (Kc) express?

  The relationship between concentrations of reactants and products
• What does a large Kc value indicate?

  Equilibrium lies to the right, more products
• What does a small Kc value indicate?

  Equilibrium lies to the left, more reactants
• What primarily affects Kc?


  Temperature
• What is the expression for Kc?

  Kc = [products] / [reactants]
• What is the initial moles of products in a reaction?

  Always 0 as the reaction hasn’t started
• What happens to Kc in an exothermic reaction with increased temperature?

  Kc decreases as equilibrium shifts left
• What happens to Kc in an exothermic reaction with decreased temperature?

  Kc increases as equilibrium shifts right
• What happens to Kc in an endothermic reaction with increased temperature?

  Kc increases as equilibrium shifts right
• What happens to Kc in an endothermic reaction with decreased temperature?

  Kc decreases as equilibrium shifts left
• How do catalysts affect Kc?

  Kc is not affected by catalysts
• What does the term dynamic equilibrium state?

  The forward and backward reactions proceed at equal rates

  The concentrations of reactants and products remain constant
• How do catalysts benefit industrial processes?

  Lower costs as speeds up the rate allowing lower temperatures to be used