1. EQUILIBRIA 2 types : 1)Chemical equilibrium (AS) Dynamic equilibrium
Equilibrium constants and calculations
Factors affecting equilibrium
Industrial applications
2)Ionic equilibrium (AS and A2)

2. Dynamic equilibrium
1)Equilibrium occurs when 2 opposing forces occur at the same rate
Eg :
Physical equilibrium : H2O (l)  H2O (g)
Chemical equilibrium : N2O4 (g)  2NO2 (g)
2)Dynamic  changing
Reactants keep changing into products
and products keep changing back into reactants

3. STATIC EQUILIBRIUM

4. Dynamic equilibrium

5. Chemical equilibrium Types of chemical reactions
1. Irreversible reactions :
Reactions which occurs in one direction only
Usually products are formed with no reactants left ( unless one reactant is in excess)

6. Eg :
2Mg O2  2MgO
BaCl2 + H2SO4  BaSO HCl

7. 2. Reversible reactions :
Reactions can occur in two directions
At the end of the reaction, both reactants and products are present ( at equilibrium )

8. Eg :
N H2 2NH3
2SO2 + O2  2SO3

9. Dynamic equilibrium Consider the following reversible reaction :
A B C + D
reactants products
Forward reaction
Reverse/backward reaction

10. Note : rate of reaction is proportional to concentration of reactants
1. Initially on mixing:
a. Forward reaction: A + B  C + D
i) [A] and [B] are high , rate of rxn is high/fast
ii) With time, [A] and [B] decreases therefore rate decreases

11. b. Reverse reaction : C + D  A + B
i) rate of reverse rxn is zero as no C and D exist
ii) with time, as more C and D are formed, rate will increase

12. 2. At equilibrium,
a. there will come a time when rate of forward reaction equals the rate of the reverse reaction
b. System is said to have achieved equilibrium
c. This equilibrium is said to be dynamic
 even after equilibrium has been reached, the two reactions continue to proceed at equal rates

13. d. Concentrations of A, B , C and D will be constant
A and B are being reformed in the reverse reaction at the same rate as they are reacting together in the forward reaction

14. 3. These changes can be represented graphically :
a. change in rate of forward and reverse reaction

16. b. change in concentration of reactants and products
Eg :

19. time

20. Note :
Non-reversible reaction ( with no reactant in excess )

21. concentration

22. 4. Characteristic features of a dynamic equilibrium:
a. rate of forward reaction equals rate of reverse reaction **
b. reaction is continuous *
c. concentrations of all products and reactants are constant ( NOT necessarily equal ) *

23. d. The equilibrium can be achieved from either direction
e. The equilibrium can only be achieved in a closed system
A closed system is one in which there is absolutely no loss or gain of materials to or from the surroundings
Eg : CaCO3 (s)  CaO(s) + CO2(g)