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
Endothermic
reaction
energy is treated as one of the reactants/products
increase in temperature → reaction shifts to LEFT
- equivalent of adding a component
decrease in temperature → reaction shifts to RIGHT
- equivalent of removing a component
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
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