Topic 7 and 17 - Equilibrium
Topic 7.1 - Equilibrium
Equilibrium is reached in a closed system when rate of forward and reverse reactions are equal and concentrations of products and reactant remains unchanged
Reversible reaction - products can react to re-form reactants
In Physical Systems
Chemical reaction is not occurring.
Equilibrium only occurs in closed system - no matter is exchanged with surroundings
E.g. evaporation-condensation cycle
In Chemical System
Chemical reaction is occuring
forward reaction must equal reverse reaction
Characteristics of Equilibrium
- Equilibrium is dynamic - processes are still occurring even when concentration is constant
2. Equilibrium is achieved in closed system
3. Concentration of reactants and products remains constant
4. No macroscopic change in properties - observable properties do not change
5. Equilibrium can be reached from either direction
6. Concentrations of reactants and products are not necessarily equal
Equilibrium Position
Proportion of reactants and products
Mostly products - Lies to the right, Kc is large
Mostly reactants - Lies to the left, Kc is small
Kc = Equilibrium constant
jA + kB <----> lC + mD
K = [C]l [D]m / [A]j [B]k
Solids and liquids are not included in K expression
The magnitude of the equilibrium constant indicated the extent of a reaction at equilibrium and is temperature dependents
Relationships
Reaction Quotient Q
When Kc of reaction = x , Kc of reverse reaction = 1/x
When a balanced equation is multiplied by n, Kc = Original Kc^n
If you add reactions A and B, Kc = (Kc of A) x (Kc of B)
Relative amount of products / reactants present at a particular point.
non-equilibrium concentrations
Changes in concentration, pressure and temperature affect equilibrium.
calculated form time t with same expression as Kc
Q = K - Equilibrium
Q > K - System shifts to left until equilibrium is achieved
Q < K - System shifts right until equilibrium is achieved