Chemical equilibrium
JEE Syllabus
Chemical equilibrium:
Law of mass action;
Equilibrium constant,
Le Chatelier's principle (effect of concentration, temperature and pressure); Significance of ΔG and ΔGo in chemical equilibrium;
Solubility product, common ion effect,
pH and buffer solutions;
Acids and bases (Bronsted and Lewis concepts);
Hydrolysis of salts.
The syllabus has two main components: Equilibrium among ions and equilibrium among compounds
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There are reactions where one can see the reverse action also to be active and see the equilibrium point. In this case
A + B → C + D and
C+D → A+B both reactions keep taking place.
At the point of equilibrium the rate of both reactions is same. Formation of A+B is equal to consumption of A+B.
Rate of forward reaction = k-f[A][B]
Rate of reverse reaction or backward reaction = k-r[C][D]
Therefore k-f[A][B] = k-r[C]{D]
This gives k-f/k-r = [C]{D]/[A][B]
The equilibrium constant is always written as products by reactants.
For the a general reaction
aA + bB ↔ cC+dD (Normal two arrows are used for reversible reaction. Only one arrow with heads on both sides is used here to tide over the inability to show two arrows.)
k-eq = [C]^c[D]^d/[A]^a[B]^b
The equilibrium constant may or may not have units.
In the case of 2A ↔ 2B +C
The units of equilibrium constant are going to be: (mol/l)^2(mol/l)/(mol/l)^2
= mol/l
Ionic Equilibrium – Introduction
Acids, basess and salts when dissolved n water dissociate to some extent and form ions. In the ion formation, an equilibrium is established between ionized and unionized (whole) molecules as this ionization is a reversible reaction. Such an equilibrium that involves ions is called ionic equilibrium.
Acids and bases definitions (Arrhenius, Bronsted and Lewis)
Arrhenius defined acid as a hydrogen compound which in water solution give hydrogen ions.
He defined base as a hydroxide compound which in water solution gives hydroxide ions.
Lowry and Bronsted
An acid is defined as a substance having a tendency of lose or to donate one or more protons.
A base is defined as a substance having a tendency to accept or add a proton
Lewis Theory of Acids and Bases
Acid: An acid is any substance (molecule, ion or atom) that can accept a lone pair of electrons to form a coordinate bond (*Remember coordinate bond and lone pair topics in chapter on Bonding)
Base: Base is any species (molecule, ion or atom) that can donate a lone pair of electrons to form a co-ordinate bond.
Ostwald’s Dilution law
α = SQRT(K/C)
α = Total mole of acid or base dissociated/Total mole of acid or base present in the solution
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