equilibrium 1

• What are reversible reactions?

  Reversible reactions are reactions in which the products can react together to reform the original reactants.
• How are reversible reactions represented?

  They are represented using a double arrow.
• What characterizes the reactions in a reversible reaction system?

  One reaction will be endothermic and the opposite reaction will be exothermic.
• What is dynamic equilibrium?

  Dynamic equilibrium occurs when the rate of the forward reaction is equal to the rate of the backward reaction.
• What happens to the concentrations of reactants and products at dynamic equilibrium?

  The concentrations of the reactants and products remain constant.
• In what type of system can dynamic equilibrium occur?

  Dynamic equilibrium can only occur in closed systems where no substances can get in or out.
• What does Le Chatelier’s principle predict?

  Le Chatelier’s principle predicts how an equilibrium mixture will change if the reaction conditions are altered.
• What does Le Chatelier’s principle state about a system subject to change?

  When a system is subject to change, the system will alter to lessen the effect of that change.
• How can altering reaction conditions be useful in industry?

  Altering reaction conditions can maximize the yield of a desired product.
• What effect does increasing temperature have on an endothermic reaction?

  Increasing temperature favors the endothermic reaction as the excess heat needs to be removed from the system.
• What happens to the yield of endothermic products when temperature is increased?

  The yield of the endothermic products will increase.
• What effect does decreasing temperature have on an exothermic reaction?

  Decreasing temperature favors the exothermic reaction as heat needs to be gained.
• What happens to the yield of exothermic products when temperature is decreased?

  The yield of the exothermic products will increase.
• In exam questions, what will be given to clarify which direction is endothermic and which is exothermic?

  The ∆H of the forward reaction will be given.
• What effect does increasing pressure have on a reaction?

  Increasing pressure favors the side of the reaction with fewer moles of gas.
• What happens to the yield of products when pressure is increased?

  The yield of the products on the side of the reaction with the fewest moles of gas will increase.
• What effect does decreasing pressure have on a reaction?

  Decreasing pressure favors the side of the reaction with more moles of gas.
• What happens to the yield of products when pressure is decreased?

  The yield of the products on the side of the reaction with more moles will increase.
• What effect does increasing the concentration of reactants have on a reaction?

  Increasing the concentration of the reactants will favor the reaction direction that produces the products.
• What happens to the yield of products when the concentration of reactants is increased?

  The yield of the products will increase.
• What happens when the concentration of products is decreased?

  Decreasing the concentration of products will favor the reaction that reforms the reactants.
• How do catalysts affect the equilibrium position?

  Catalysts appear not to affect the equilibrium position as they affect the forward and backward reaction equally.
• What is the effect of catalysts on the rate of reaching equilibrium?

  Catalysts allow equilibrium to be reached faster.
• What is the equilibrium constant denoted as?

  The equilibrium constant is denoted as Kc.

  
• What does Kc indicate for a reaction?

  Kc indicates the position of equilibrium for a reaction at a certain temperature.
• When does the value of Kc change?

  Kc changes when the reaction conditions are changed, which in turn changes the position of equilibrium.
• What is needed to find the value of Kc?

  The concentrations of the reactants and products at equilibrium need to be known.
• How is Kc calculated?

  Kc is equal to the concentration of the products divided by the concentration of the reactants.

  
• How are the concentrations of substances represented in the Kc expression?

  Any variation in the number of moles raises that substance to a power with the same value as the number of moles.
• What affects the units of Kc?

  The equilibrium constant has varying units depending on the chemical reaction.
• How can Kc be calculated from the units?

  Kc can be calculated by substituting the units into the Kc expression.
• What factors affect the value of Kc?

  The value of Kc is not affected by concentration change or use of a catalyst, but it is affected by changing the reaction temperature.
• What is the compromise between rate of reaction and product yield?

  A condition change that produces a higher proportion of the product may also reduce the rate of the reaction.
• How can reaction conditions affect both product yield and rate of reaction?

  Reaction conditions can shift the position of the equilibrium to favor the production of either the products or the reactants.
• What happens when the temperature is decreased in a forward endothermic reaction?

  Decreasing the temperature would increase the product yield but decrease the rate of reaction.
• What must be considered in industry when a factor increases product yield but decreases the rate of reaction?

  A compromise must be made to achieve both a relatively good product yield and a relatively fast rate of reaction.

  
• Why is it important to select reaction conditions that provide both good product yield and fast rate of reaction?

  If only product yield is taken into account, the rate of reaction would occur so slowly that the product is not made at a useful rate.

  
• What are the effects of changing temperature, pressure, and concentration on equilibrium according to Le Chatelier's principle?

  • Increasing temperature favors endothermic reactions, increasing yield of endothermic products.
  • Decreasing temperature favors exothermic reactions, increasing yield of exothermic products.
  • Increasing pressure favors the side with fewer moles of gas, increasing yield of products on that side.
  • Decreasing pressure favors the side with more moles of gas, increasing yield of products on that side.
  • Increasing concentration of reactants favors product formation, increasing yield of products.
  • Decreasing concentration of products favors reactant formation, increasing yield of reactants.

  
• What are the key points regarding catalysts and equilibrium?

  • Catalysts do not affect the equilibrium position.
  • Catalysts affect both forward and backward reactions equally.
  • Catalysts allow equilibrium to be reached faster.
• What are the key aspects of the equilibrium constant (Kc)?

  • Kc indicates the position of equilibrium at a certain temperature.
  • Kc changes with reaction conditions but not with concentration changes or catalysts.
  • Kc is calculated from the concentrations of reactants and products at equilibrium.
  • The units of Kc vary depending on the reaction.