Reversible Reactions and Le Chatelier's Principle
equilibrium - when the forwards reaction is going at exactly the same rate as the backwards one
reversible reactions
as the forwards reactants react their concentrations fall so it will slow down but as more and more products are made their concentrations rise, the backwards reaction will speed up
after a while the system will be at eqilibrium
at equilibrium both reactions are still happening but there is no overall effect as they have reached a balance and wont change
equilibrium can only be reached if the reversible reaction takes place in a closed system
position of equilibrium
when a reaction is at equilibrium it doesn't mean the amount of reactants and products are equal
lies to the right - concentration of products is greater than the reactants
lies to the left - concentration of reactants is greater than the products
the position depends on:
- temperature
- pressure
- concentration
endo / exothermic
in reversible reactions if it is endothermic one way it will be exothermic in the other
energy transferred from the surrounds by endothermic reaction = energy transferred to the surrounding during the exothermic reaction
Le Chatelier's Principle
the idea that if you change the conditions of a reversible reaction at equilibrium the system will try to counteract that change
temperature
if you decrease the temperature the equilibrium will move in the exothermic direction to produce more heat. This means you get more products for the exothermic reaction and fewer products for the endothermic reaction
pressure
if you increase the pressure the equilibrium tries to reduce it - it moves in the direction where there are fewer molecules of gas
if you decrease the pressure the equilibrium tries to increase it - it moves in the direction where there are more molecules of gas
concentration
if you change the concentration of either of the reactants or products the system will no longer be at equilibrium
if you increase the concentration of the reactants the system tries to decrease it by making more products
if you decrease the concentration of products the system tries to increase it again by reducing the amount of reactants