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

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

STATIC EQUILIBRIUM

Dynamic equilibrium

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)

Eg : 2Mg + O2  2MgO BaCl2 + H2SO4  BaSO4 + 2HCl

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

Eg : N2 + 3H2 2NH3 2SO2 + O2  2SO3

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

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

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

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

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

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

b. change in concentration of reactants and products Eg :

time

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

concentration

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 ) *

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)