NO2 to N2O4 Teacher Notes

  NO2  (g)     ⇄  N2O4(g)     NOTICE  THE  EQUILIBRIUM  SHIFTING  BACK  AND  FORTH!       We  observe  the  Dynamic  Chemical  Equilibrium  through  this   MACROSCOPIC  PROPERTY:     dark  brown  gas     ⇄   light  brown  gas     (or  colourless)       NO2  (g)       ⇄     N2O4(g)   hot water cold water                 EFFECT  OF  TEMPERATURE  ON  REACTION  EQUILIBRIA     ACTIVATION  ENERGY  DIAGRAM  FOR  THIS  REACTION:   If  N2O4(g)  predominates  in  cold  temps  and  NO2  (g)  predominates  at   high  temps,  then  the  reaction  is  EXOTHERMIC:       This  reversible  reaction  reached  a  state  of  equilibrium  and  showed  the   following  characteristics:   1)    the  system  was  closed   2)    opposite  reactions  occurred  at  the  same  rate   3)    equilibrium  was  reached  by  starting  with  either  reactants  or   products   4)    the  temperature  was  constant  (constant  at  0oC  or  constant  at  100oC)     Graphical  representation    of  the  relative  concentrations  of  NO2  and   N2O4  at  equilibrium  at  0oC  and  100oC:   where  the  30%  portion  represents  NO2  (g)     and  the  rest  represents  N2O4(g)   Graphical  representations  of  changing  concentrations  of  NO2  and  N2O4   at    100oC  as  equilibrium  is  reached:             ANALYSIS.     1)    What  macroscopic  property  did  we  observe  to  show  that  the   reaction  rate  (forward  or  reverse)  is  constant?   2)    What  macroscopic  property  did  we  observe  to  show  that   temperature  affects  an  equilibrium  reaction?       3)    Based  on  our  macroscopic  observations  or  on  graphical  information,   which  gas  predominates  at  low  temperatures?     4)    What  would  you  expect  to  happen  if  you  mixed  a  tube  containing   pure  NO2  with  another  tube  containing  pure  N2O4  at  room  temp?         ANALYSIS.     1)    What  macroscopic  property  did  we  observe  to  show  that  the   reaction  rate  (forward  or  reverse)  is  constant?   -the colour ( at 0oC or at 100oC ) remained a constant, therefore the N2O4 (or NO2) was being made at the same rate as it was being used up. 2)    What  macroscopic  property  did  we  observe  to  show  that   temperature  affects  an  equilibrium  reaction?   -the colour became lighter or darker when the temp. changed - meaning there was more or less NO2 present.   3)    Based  on  our  macroscopic  observations  or  on  graphical  information,   which  gas  predominates  at  low  temperatures?   -N2O4 predominated at low temp. -NO2 predominated at high temp.   4)    What  would  you  expect  to  happen  if  you  mixed  a  tube  containing   pure  NO2  with  another  tube  containing  pure  N2O4  at  room  temp?   -the tubes should become the same colour - eventually the two gases will reach equilibrium and attain the same constant colour.