AP Chem Ch. 13

• Equilibrium

  state in which the rate of the forward reaction = rate of reverse reaction
• Equilibrium in regards to concentration

  concentration of all reactants and products are constant
• Is equilibrium static if concentrations are not changing?

  NO! highly dynamic situation
• Why is equilibrium microscopically dynamic?

  products and reactants are constantly being formed and consumed; because the rates are equal there is not net change in concentration
• Do the concentrations of reactants at products have to be equal to one another at equilibrium?

  No the concentrations do not have to be equal at equilibrium
• What vessel must a chemical reaction be carried out in to reach equilibrium?

  closed vessel
• If the reaction favors the products where does the equilibrium position lie?

  right
• If the reaction favors the reactants where does the equilibrium position lie?

  left
• What is equilibrium position determined by?

  initial concentrations, relative energies of R and P, organization of R and P
• If the reaction is reversed?

  take the reciprocal of the old K value to get the new

  
• if balanced equation is multiplied by a factor of X

  new K value will be raised to X power

  
• when does Kp = Kc

  when sum of coefficients on each side is the same
• Homogeneous equilibria

  all substances are in the same phase
• Heterogeneous equilibria

  involve substances in more than one phase
• For heterogenous equilibrium, what is omitted from the equilibrium expression?

  pure solids, liquids
• Value of K is much larger than 1?

  at equilibrium, the reaction system will consist of mostly products; equilibrium position lies to the right; the reaction goes essentially to completion
• Very small value of K?

   the system at equilibrium will consist of mostly reactants – the equilibrium position lies to the left; forward reaction does not occur to any significant extent
• Is the size of K and the time required to reach equilibrium related?

  No
• Time to equilibrium

  depends on reaction rate; determined by the size of activation energy
• Size of K

  determined by thermodynamic factors; difference in energy between products and reactants
• If the concentrations of all reactants and products are nonzero, what is the direction of the reaction?

  direction must be calculated
• Reaction quotient

  used to predict which way the reaction will proceed
• Q = K

  no shift; system is at equalibrium
• Q > K

  shifts left; products will be consumed and reactants will be formed until equilibrium
• Q<K

  shifts right; Reactants will be consumed and products    formed, until equilibrium
• What happens if change is imposed on a system at equilibrium?

  the position of the equilibrium will shift in a direction that reduces that change
• concentration of a component increases

  system will shift away form added component
• concentration of a component decreases

  system will shift towards that component
• When does K change

  when temperature of reaction changes
• Exothermic reaction

  energy is a product
• Endothermic Reaction

  Energy is a reactant
• In an endothermic reaction what direction will equilibrium shift if temp is increased

  Right; value of K increases
• In an endothermic reaction what direction will equilibrium shift if temp is decreased

  left; K will decrease
• In an exothermic reaction what direction will equilibrium shift if temp is increased

  left; K decreases
• In an exothermic reaction what direction will equilibrium shift if temp is decreased

  right; K increases
• The addition of inert gas does not affect equilibrium position. What are these inert gases

  Argon, Neon, Helium
• What does decreasing the volume(increases pressure) do to equilibrium position

  shifts towards the side with fewer moles of gas
• What does increasing the volume(decreases pressure) do to equilibrium position

  shifts towards side with more moles of gas
• Le Chatellier's principle

  decrease in volume will cause the system to reduce it's own volume; shift to direction with less moles
• What does a catalyst do?

  lower activation energy for both forward and reverse reaction; neither side is favored