4d) Equilibria

Some reaction are reversible which means that they have the same rate backwards and forwards
That means that there is no overall change: reactants --> products    products --> reactants

This can only take place in a CLOSED system or it would escape. Initially there are no products when you first start to mix the reactants. After a while there will be products; but still more reactants. With time the reactants go down and the products go up and we reach the SAME RATE, this is called DYNAMIC EQUILIBRIUM.
The position of equilibrium is not always at the half way point therefore there could be a position where there is more reactants than products.

Dehydration of hydrated copper (II) sulfate:
hydrated copper(II) sulfate + heat   anhydrous copper(II) sulfate + water

Heat makes the reaction go forwards (endothermic), whilst cold water makes it go backwards (exothermic) 

Effect of heat on ammonium chloride:

ammonium chlorideammonia + hydrogen chloride

Ammonium chloride decomposes when it is heated so the forward reaction is endothermic, whilst the backwards reaction is exothermic 

Factors which influence equilibrium:

• Temperature increase
• moves the equilibrium to the right hand side, in the direction that produces the fewer molecules/moles of gas on the RHS  
• Pressure increase
• moves equilibrium to the right hand side, moves into the direction that absorbs heat energy e.g. endothermic reactions 
• Concentration 
• Catalyst to get products or reactants faster 

 

LHS              RHS 

A + B  C + D