CHEM 132, Chapter 12

• Equilibrium


  The state where there are no observable changes as time goes by
• Chemical equilibrium


  Achieved when the rates of the forward and reverse reactions are equal and the concentration of reactant and products remain constant
• Equilibrium position


  A set of equilibrium concentrations
• Systems only have one equilibrium constant at a particular temperature, but has an infinite number of equilibrium positions
• Specific equilibrium position adopted by the system depends on initial concentrations
• Homogeneous equilibria


  When all reactants and products are in the same phase
• Heterogeneous equilibria


  When reactants and products are in more than one phase
• Position of heterogeneous equilibria does not depend on amounts of pure solids or liquids
• Equilibrium constant


  Can help predict tendency of reaction to occur, if a set of concentrations represents an equilibrium condition or equilibrium position that will be achieved from a set of initial conditions
• If equilibrium lies to the right

  K is large
• If equilibrium lies to the left

  K is small
• Reaction quotient, Q


  The law of mass action using any concentrations instead of equilibrium concentration
• If Q=K


  The system is at equilibrium
• If Q>K


  The system will shift left
• If Q<K


  The system will shift right
• If an external stress is applied to a system at equilibrium


  The system adjusts in a way to reduce the stress and reach a new equilibrium
• Increasing concentration


  Shifts equilibrium to the other side
• Decreasing concentration


  Shifts equilibrium to its side
• Increasing pressure/decreasing volume


  Shifts equilibrium to side with fewest moles of gas
• Decreasing pressure/increasing volume


  Shifts equilibrium to the side with most moles of gas
• When an exothermic reaction has an increase in temperature


  It shifts to reactants (the heat is a product)
• When endothermic reactions increase in temperature


  It shifts to the products (heat is a reactant)
• Catalysts change the rate of reaction (Ea and k) but not equilibrium K
• Adding a catalyst


  Speeds the reaction up so equilibrium is reached faster, but it isn't changed