3.22C: Know the Effect of Changing Either Temperature or Pressure on the Position of Equilibrium in a Reversible Reaction: an Increase (or Decrease) in Temperature Shifts the Position of Equilibrium in the Direction of the Endothermic (or Exothermic) Reaction, an Increase (or Decrease) in Pressure Shifts the Position of Equilibrium in the Direction that Produces Fewer (or More) Moles of Gas

EFFECTS OF TEMPERATURE:

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CHANGE	HOW THE EQUILIBRIUM SHIFTS
INCREASE IN TEMPERATURE	Equilibrium moves in the endothermic direction
DECREASE IN TEMPERATURE	Equilibrium moves in the exothermic direction

Example:

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Iodine Monochloride reacts reversibly with Chlorine to form Iodine Trichloride:

                            ICl              +              Cl2              ⇌              ICl3

                      Dark Brown                                                         Yellow

When the equilibrium mixture is heated, it becomes darker brown in colour. Explain whether the backward reaction is exothermic or endothermic

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As the equilibrium mixture has become darker brown in colour, more Iodine Monochloride (ICl) has been produced, therefore shifting equilibrium to the left As increasing temperature causes equilibrium to move in the endothermic direction, the backward reaction is therefore endothermic

EFFECTS OF PRESSURE:

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CHANGE	HOW THE EQUILIBRIUM SHIFTS
INCREASE IN PRESSURE	Equilibrium shifts in direction that produces the smaller number of molecules of gas
DECREASE IN PRESSURE	Equilibrium shifts in direction that produces the larger number of molecules of gas

Example:

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Nitrogen Dioxide can form Dinitrogen Tetraoxide, a colourless gas

                            2NO2             ⇌              N2O4

                       Brown Gas                    Colourless Gas

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Predict the effect of the increase in pressure on the position of equilibrium

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Number of Molecules of Gas on the Left    =    2     Number of Molecules of Gas on the Right  =    1 As an increase in pressure causes equilibrium to shift in direction that produces the smaller number of molecules of gas, equilibrium shifts to the right