7.1 Dynamic equilibrium & 7.2 The position of equilibrium

7.1.1 Outline the characteristics of chemical and physical systems in a state of equilibrium.
Chemical systems e.g. Dissociation

Characteristics of an equilibrium
1. Dynamic equilibrium: reactions have not stopped, they're still occurring (see right)
2. Closed systems: This prevents exchange of matter with the surroundings
3. Concentrations remain constant: the products and reactants are produced and destroyed at an equal rate
4. No macroscopic properties change (no observable change): colour, density depends on concentration of the equilibrium mixture
5. Eqm can be reached from either direction: the same eqm mixture will be established under the same conditions, regardless of the starting product/reactant mixture.

Usually in an eqm mixture either products/reactants will have a higher concentration

If the eqm lies to the right = more products are being formed

If the eqm lies to the left = more reactants being formed

7.2.1 Deduce the equilibrium constant expression (Kc) from the equation for a homogeneous reaction.

7.2.2 Deduce the extent of a reaction from the magnitude of the equilibrium constant.
The magnitude of Kc determines the EXTENT of the reaction, not how fast it will achieve eqm.

If Kc >> 1, the reaction is almost to completion

If Kc << 1, the reaction hardly proceeds

7.2.3 Apply Le Chatelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant.

"A system at equilibrium when subjected to a change will respond in such a way as to minimize the effect of the change." 

- Le Chatelier's Principle on distrupting the equilibrium

CONCENTRATION

Adding reactants: eqm shifts right (in favour of the products), and a new mixture is established

Adding products: eqm shifts left (in favour of the reactants), and a new mixture is established

Removing reactants: eqm shifts left (in favour of the reactants), and a new mixture is established
Removing products: eqm shifts right (in favour of the products), and a new mixture is established


PRESSURE
Increase: favours the side with less gas molecules/moles
Decrease: favours the side with more gas molecules/moles
This changes the equilibrium, but not Kc. Kc stays the same.

TEMPERATURE
Kc is temperature dependent, a change in temperature will cause a change in Kc.

7.2.4 State and explain the effect of a catalyst on an equilibrium reaction.
A catalyst will speed up both forward AND backward reactions, therefore the eqm will not shift.

7.2.5 Apply the concepts of kinetics and equilibrium to industrial processes.