equilibrium

• what is a catalyst?

  (i.e an enzyme)

  • a substance which speeds up the rate of reaction through lowering the amount of activation energy; does not change the amount of products produced and kc.
  • allows equilibrium to be reached within a shorter period of time.
• What is a closed system?

  A system that does not allow the transfer of matter in or out
• what is dynamic equilibrium?

  • when the forward reaction and reverse reactions occur at the same rate.
• What is equilibrium in a chemical reaction?

  It is when the forward and reverse reaction rates are the same and concentrations remain unchanged
• What conditions must be met for a reaction to be in equilibrium?

  It must be a reversible reaction and in a closed system
• What is an incomplete reaction?

  When the reactants aren’t fully used up and some reactant particles remain
• What is the equilibrium constant (Kc)?

  The ratio of concentrations of products over reactants when equilibrium has been reached
• What is a reversible reaction?

  When reactants react into products and those products can react back into the original reactants
• What is the equilibrium expression formula?

  Kc = $[C]^c[D]^d / [A]^a[B]^b$
• Why are liquids and solids not included in the equilibrium expression?

  Because their concentration is constant
• What does it mean if Kc is greater than 1?

  The products will be favored in the forward reaction
• What does it mean if Kc is less than 1?

  The reactants will be favored in the reverse reaction
• How do you find a missing concentration when Kc is known?

  Put the missing concentration as 'x' and solve linearly
• What is Le Châtelier’s principle?

  If a chemical system at equilibrium experiences a change, the equilibrium shifts to counteract the change
• How does temperature affect equilibrium?

  The equilibrium will shift in the endothermic or exothermic direction depending on the need to heat or cool
• What happens if the equilibrium is endothermic?

  It will favor the endothermic direction to cool down and the exothermic direction to heat it
• What happens if the equilibrium is exothermic?

  It will favor the exothermic direction to heat up and the endothermic direction to cool it
• What can alter the value of Kc?

  Only a change in temperature can alter the value of Kc
• How can the change to Kc at a higher temperature be used?

  It can predict which process (forward or reverse) is favored with an increase in temperature
• What happens if more NO2 is introduced into the system?

  The position of the equilibrium will shift to reduce the increased concentration of NO2
• What happens if the concentration of one side is increased?

  The equilibrium will favor the opposite side to re-establish equilibrium
• What happens if the concentration of one side is decreased?

  The equilibrium will shift to increase the opposite side
• What happens when pressure on an equilibrium is decreased?

  The equilibrium will shift to favor the side with the most molecules of gas
• What happens when pressure on an equilibrium is increased?

  The equilibrium will shift to favor the side with the least molecules of gas
• How do catalysts affect equilibrium?

  Catalysts affect the speed of both the forward and reverse reactions but do not change the position of equilibrium
• What happens to the concentrations of equilibrium with a catalyst?

  The concentrations of the equilibrium will stay the same with or without the catalyst
• When does Kc change?

  Kc only changes when the temperature of the equilibrium changes
• dynamic Equilibrium



  • a type of equilibrium where the rates of forward and reverse reactions are not zero, but are equal, resulting in a stable state.
• Le Chatelier's Principle



  • when a stress is applied to a system at equilibrium, the system responds by shifting the equilibrium to counteract the stress.
• +ive ΔH


  endothermic; heat energy is being absorbed

  • products will have more energy than reactants
  • heat = reactants in endothermic reactions
  • shifts equilibrium to the right/ products
• -ive ΔH


  exothermic reaction; heat is being released

  • products will have less energy than reactants
  • heat = products
  • increase in temperature = shifts equilibrium to the left/ reactants
• what happens to Kc when temperature increases in exothermic reactions?

  -ive ΔH, Kc decreases as temperature increases (as there are more products), and products would be favored

  • products favored = reverse (endothermic) reaction would be favored as P>R, to counteract increase of temp
  • increasing reactants and decreasing products
• what happens to Kc when temperature increases in endothermic reactions?


  +ive ΔH, Kc increases as temperature increases (as there are more reactants), and reactants would be favored.

  • reactants favored = forward (exothermic) reaction would be favored as R>P
  • producing more products and decreasing reactants, making Kc increase.
• what only affects equilibrium constant? 


  change in temperature
• what increases the yield of products?


  • removing products, as R>P, favoring the forward reaction and increasing amount of products produced
  • prevents products from turning back into reactants