15.2: Le Châtelier’s Principle

 can predict how certain changes in a reaction will affect the position of equilibrium  when a chemical system at equil. is disturbed by a change in the system, the system will react in a direction opposing the change until a new equil. is reached

 he described a 3 stage process  Initial equilibrium  Shifting non-equilibrium  New equilibrium  Catalysts can be used to decrease the time to reach the new equil. position does not affect the final position of that equilibrium

 system will shift away from the added component or towards a removed component  a change in conc. of a pure solid or liquid does not cause an equil. shift  Ex: N 2 + 3H 2  2NH 3  if more N 2 is added, then equilibrium position shifts to the right  if some NH 3 is removed, then equilibrium position shifts to the right

 adding or removing gaseous reactant or product is same as changing conc.  adding inert or uninvolved gas  increase the total pressure  doesn’t effect the equilibrium position

 changing the volume  decrease V decrease in # gas molecules shifts towards the side of the reaction with less gas molecules  increase V increase in # of gas molecules shifts towards the side of the reaction with more gas molecules

 all other changes alter the concentration at equilibrium position but don’t actually change value of K  value of K does change with temperature

 if energy is added, the reaction will shift in direction that consumes energy  treat energy as a:  reactant: for endothermic reactions  product: for exothermic reactions

 add CO  to left  add C  no shift  remove C  no shift  add As 4 O 6  no shift  remove As 4 O 6  no shift  remove As 4  to right  decrease volume  to left  add Ne gas  no shift

 decrease volume  to right  increase volume  to left  add P 4  no shift  remove Cl 2  to left  add Kr gas  no shift  add PCl 3  no shift

 endo or exo?  endothermic  increase temp  to right  increase volume  no shift  decrease temp  to left

 Textbook p695 #1-3, LSM 15.2J  LSM summary 15.2C,D,F