CO_2(aq)          D           CO_2(g)

• No bubbles are seen as carbon dioxide gas is dissolved.
• The conditions are fixed and no matter is exchanged.
• The dissolved gas and the gas above the liquid is in dynamic equilibrium.

• Open the bottle and the pressure drops.
• Dissolved carbon dioxide is released from the liquid as gas.
• The forward reaction is faster than the reverse reaction until equilibrium is re established - goes flat!!
• There are actually 4 equilibrium involved in this concept and are too complex to look at in detail now.

• As the HCl dissolves in water that volume of gas has been removed from the flask.
• Water is drawn up to replace that volume of gas removed.
• The fountain gradually becomes less vigorous as the water reaches saturation:

                                  HCl_(g)   D    HCl_(aq)

• When the reaction appears to have finished does this mean that no more gas dissolves in the water?
• At equilibrium we say that the rate of the forward and reverse reaction occurs at the same rate.
• This means that the concentrations of the reactants and products are the same.
• There is no observable change.
• This is described as DYNAMIC.
• The extent of how far the reaction has gone towards the products is called 'the position of the equilibrium'
• Equilibrium is stable under fixed conditions and in an isolated system:

              Fixed conditions:  Temperature and pressure remains the same.

              Isolated system:    No material is added or removed from the system