Equilibrium
Definition
A state in which opposing forces or influences are balanced.
Examples
Effect of heat on ammonium chloride
Dehydration of hydrate copper sulphate
When you add water to copper sulphate, hydrated copper sulphate is formed
When water is removed you get dehydrated (anhydrous) copper sulphate
REVERSIBLE REACTION
If you heat ammonium chloride it splits up into ammonia and hydrogen chloride.
Hydrogen chloride and ammonia can be reacted to form ammonium chloride.
REVERSIBLE REACTION
Neither reactions have stopped, both are reacting at the same speed.
It’s like walking the wrong way on an escalator.
“At equilibrium the concentrations of the reactants and products are constant but not necessarily equal.” (BBC Bitesize)
Dynamic equilibrium
The forward and backward reactions occur and the same time and never stop.
When the rate of the forward reaction is the same as the reverse reaction, the reaction is said to have reached equilibrium.
If a catalyst where to be used, the reaction would reach equilibrium much sooner.
Open and closed systems
Open sytems
Closed systems
A closed system is when a reaction happens in a closed environment (such as a container), meaning that none of the reactants or products can escape.
An environment where products and reactants can escape
Reversible reactions that happen in a closed system eventually reach an equilibrium.
Reactions that happen in an open system would never reach equlibrium
Shifting equilibrium
If we make changes to the concentration, pressure or temperature of the reaction then the position of the equilibrium can be altered.
Any change made to a reaction which is in equilibrium, will result in the equilibrium position moving to minimize the change made
E.g. changing the concentration
The following equilibrium is formed when chlorine dissolves in water:
Cl2(g) + H2O(l) <-----> Cl-(aq) + ClO-(aq) + 2H+(aq)
If potassium chloride (a source of chloride ions) is added to the equilibrium mixture, the equilibrium will shift to the left, to remove the chloride ions added.
If potassium hydroxide is added, the hydroxide ions will react with the hydrogen ions and remove them from the mixture. The equilibrium will now move to the right, to replace the lost hydrogen ions.
Le Chatelier's Principle
A 'law' to make chemical reactions more productive
Whenever a system in equilibrium is disturbed the system will adjust itself in such a way that the effect of the change will be nullified.