REVERSE REACTIONS
a chemical reaction that can go forwards or backwards depending on the conditions
attachment ox oxygen to haemoglobin, Haber-Bosch process, thermal decomposition of ammonium chloride
SIMPLE REACTIONS that are reversible by changing the conditions
HYDRATED SALT
REFORMATION BY ADDING WATER TO DEHYDRATED POWDER
DYNAMIC EQUILIBRIUM
Forward and backward reactions take place at the same time
CLOSED SYSTEM - reactants combine into products, products break apart turning back to reactants - SAME RATE
concentration of products and reactants is constant
The system has reached a
dynamic equilibrium
The equilibrium constant defines the position of equilibrium and the progress of a reaction
alta concentrazione del prodotto e bassa del regente = equilibrio spostato a destra, reazione pressoché completa
concentrazione del prodotto e del reagente molto simile = reazione con resa di circa il 50%
bassa concentrazione del prodotto ed alta concentrazione del reagente = equilibrio spostato a sinistra - pochissimo prodotto
Chemical equilibrium controlled by:
Le Chatelier's principle
If a system at equilibrium is perturbed by an external action, it reacts in such a way as to restore the equilibrium, reducing or cancelling the effect of the perturbation
CONCENTRATION OF SUBSTANCES
TEMPERATURE
PRESSURE
The addition or subtraction of a species (reactant or product) temporarily destroys the
equilibrium state
the system reacts in such a way as to consume part of
the added species - value of K constant
catalyst does not influence the equilibrium position while it acts on the rate, accelerating both forward and reverse reactions
causes the value of the equilibrium constant to vary
each temperature has different value of K and different concentrations of reactants and products at equilibrium
supplying heat to a system favors the reaction which proceeds in the direction involving heat absorption
if the reaction towards the right is endothermic, supplying heat will favor the formation of products
if the reaction to the right is exothermic, by supplying heat the reaction will go back
Endothermic reaction
The increase in pressure of a gaseous system at equilibrium involves a shift of the
equilibrium in the direction in which there are fewer molecules
Opposite for decrease