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Reversible Chemical Reactions BIOB111 Session 4 (Le Châtelier's…
Reversible
Chemical
Reactions
BIOB111
Session 4
Reversible
Chemical
Reaction
can proceed in both directions
need to consider what forces the reaction to go backwards/forwards
Chemical
Equilbrium
the state in which forward and reverse reactions occur simultaneously at the same rate
concentrations of reactants and products no longer change
(amounts of products and reactants don't have to be equal)
Dynamic equilibrium
there is frantic activity, things are moving around
reactions are still proceeding
Le Châtelier's Principle
if
stress
is applied to a system in dynamic equilibrium the
system will adjust in the direction
that
best reduces stress
, reaching a new equilibrium
when the equilibrium disruption leads to the formation of
more products
than reactants - equilibrium will shift to the
LEFT
e.g. add more product. Will start to use the product at a higher rate, therefore increase reverse reaction
when the equilibrium disruption causes the formation of
more reactants
than products - the equilibrium will shift to the
RIGHT
e.g. add more reactants. Will cause rate of the forward reaction to use up extra reactants
more products = left
more reactants = right
Concentration
change
addition
of any component (reactant or product) shifts the equilibrium to the
opposite side
removal
of any component (reactant or product) shifts the equilibrium to the
same side
Temperature
change
Exothermic
reaction
increase
in temperature → reaction shifts to
LEFT
equivalent of adding a component
decrease
in temperature → reaction shifts to
RIGHT
equivalent of removing a component
Endothermic
reaction
increase
in temperature → reaction shifts to the
RIGHT
equivalent of adding a component
decrease
in temperature → reaction shifts to the
LEFT
equivalent of removing a component
energy is treated as one of the reactants/products
Catalysts
no effect on the position of the equilibrium
will help the system reach equilibrium faster
increase reaction rates in both forward and reverse reactions - lower activation energies
Pressure
changes
only affect chemical reactions in
gaseous state
ONLY
has an affect if the
number of moles changes
in the reaction
Pressure increase = volume decrease
equilibrium will shift towards side with
smaller number of moles
Pressure decrease = volume increase
equilibrium will shift towards side with
greater number of moles
