Equilibrium
Equilibrium is the state of a process in which the properties like temperature, pressure, and concentration etc of the system do not show any change with passage of time.
=> In all processes which attain equilibrium, two opposing processes are involved.
=> Equilibrium is attained when the rates of the two opposing processes become equal.
=> If the opposing processes involve only physical changes, the equilibrium is called Physical Equilibrium.
=> If the opposing processes are chemical reactions, the equilibrium is called Chemical Equilibrium.
Physical Equilibrium
=> Solid – liquid Equilibrium: H2O(s) = H2O(l)
=> Liquid – Gas Equilibrium: H2O(l) = H2O(g)
=> Solid – Solution Equilibrium: Salt(Solid) = Salt(in solution)
=> Gas –Solution equilibrium: CO2(g) = CO2(in solution)
Equilibrium in Chemical Process
Reversible reaction:
=> A reaction in which not only the reactants react to form the products under certain conditions but also the products react to form reactants under the same conditions
Examples:- 3Fe(s) + 4H2O(g) \rightleftharpoons Fe3O4(s) + 4H2(g)
Irreversible reaction:
=> A reaction cannot take place in the reverse direction, i.e. the products formed do not react to give back the reactants under the same condition.
Example:- AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(g)
Characteristics of Equilibrium State
=> It can be attained only if the reversible reaction is carried out in closed vessel.
=> It can be attained from either side of the reaction.
=> A catalyst can hasten the approach of equilibrium but does not alter the state of equilibrium.
=> It is dynamic in nature i.e. reaction does not stop but both forward and backward reactions take place at equal rate.
=> Change of pressure, concentration or temperature favours one of the reactions (forward or backward) resulting in shift of equilibrium point in one direction.
=> Law of Mass Action & Equilibrium Constant
=> “The rate at which a substance reacts is directly proportional to its active mass and rate of a chemical reaction is directly proportional to product of active masses of reactants each raised to a power equal to corresponding stoichiometric coefficient appearing in the balanced chemical equation”.
- * For reaction aA + bB \rightleftharpoons cC + dD
- * Rate of reaction ∝ Aa.Bb
- * or rate of reaction = KAaBb
=> where K is rate constant or velocity constant of the reaction at that temperature.
=> Unit of rate constant (K)
K = \frac{Rate\ of\ reaction}{A^aB^b}=\frac{molL^-^1 s^-^1}{(molL^1^)^a^+^b } = (molL^-^1)^1\ ^t^o\ ^n\ s^-^1
Ionic Product:
a) Product of ionic concentration due to ions already present in water or from a salt.
b) I.P. may be and may not be equal to Ksp.
c) If ionic Product (IP) > Ksp ; precipitation takes place till I.P. equals Ksp
d) If Ionic Product < Ksp ; a precipitate will not be formed and the solution will be unsaturated.
e) If Ionic Product = Ksp ; a precipitate will not form an the solution is satuated in that salt.