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CHAPTER-7EQUILIBRIUM
Equilibrium state- When rate of formation of a product in a process is in
competition with rate of formation of reactants, the state is then named as
“Equilibrium state” .
Equilibrium in physical processes: solid ⇌ liquid ⇌ gas
H2O(s )⇌ H2O(l) ⇌ H2O(vap)
Law of chemical equilibrium: At a given temperature, the product
ofconcentrations of the reaction productsraised to the respective
stoichiometriccoefficient in the balanced chemicalequation divided by the
product ofconcentrations of the reactants raised totheir individual
stoichiometric coefficientshas a constant value. This is known asthe
Equilibrium Law or Law of ChemicalEquilibrium.
aA +bB⇌cC + dD
Kc =[C]c [D]d/[A]a [B]b
Chemical equation Equilibriumconstant
aA + b B⇌c C + D K
cC + d D⇌a A + b B K′c=(1/Kc)
na A + nb B ⇌ncC + ndD K′″c= (Kcn)
Concentrations or partial pressure of pure solids orliquids do notappear in the
expression of the equilibriumconstant. In the reaction,
Ag2O(s) + 2HNO3(aq) ⇌2AgNO3(aq) +H2O(l)
If Qc >Kc, the reaction will proceed in thedirection of reactants (reverse
reaction).If Qc <Kc, the reaction will proceed in thedirection of the products
(forward reaction)
Kp is equilibrium constant in terms of partial pressure of gaseous reactants and
products.
Kc is equilibrium constant in terms of molar concentration of gaseous
reactants and products.
Kp =Kc (RT)∆n here R is gas constant, T is temperature at which the
process is carried out &∆n is no. of moles of gaseous product minus no. of
moles of gaseous reactants.
If Kc> 103; Kc is very high i.e. the reaction proceeds nearly to completion.
If Kc<103; Kc is very small i.e. the reaction proceeds rarely.
If Kcis ranging in the range of 103 to 10-3; i.e. reactants and products are just
in equilibrium.
ΔG0 = – RT lnK or ΔG0 = – 2.303RT log K
Factors affecting equilibrium constant:- temperature, pressure, catalyst and
molar concentration of reactants and products.
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, Le Chatelier’s principle:- It states that a change in any of the factors
thatdetermine the equilibrium conditions of asystem will cause the system
to changein such a manner so as to reduce or tocounteract the effect of the
change.
Arrhenius acids are the substances that ionize in water to form H+.
Arrhenius bases are the substances that ionize in water to form OH-.
Lewis acids are lone pair (of e-) accepters while Lewis bases are lone pair
donators.
Proton donor are acids while proton accepters are bases(Bronsted-Lowry
concept).
The acid-base pair thatdiffers only by one proton is called a conjugateacid-
base pair. IfBrönsted acid is a strong acid then itsconjugate base is a weak
base and viceversa.
Ionic product of water.Kw = [H+][OH–]
pH = -log [H+] ; here[H+] is molar concentration of hydrogen ion.
pH + pOH =14
pKa + pKb =14
Ka x Kb = Kw = ionic product of water=1 x 10-14
Buffer solution :The solutions which resist change in pH on dilution or with
the addition of small amounts of acid or alkali are called Buffer Solutions.
common ion effect: It can be defined as a shift in equilibrium on adding a
substance that provides more of an ionic species already present in the
dissociation equilibrium.
Hydrolysis of Salts: process of interaction between water andcations/anions or
both of salts is calledhydrolysis.
The cations (e.g., Na+, K+,Ca2+, Ba2+, etc.) of strong bases and anions(e.g., Cl–,
Br–, NO3–, ClO4– etc.) of strong acids simply get hydrated but do not
hydrolyse, andtherefore the solutions of salts formed fromstrong acids and
bases are neutral i.e., theirpH is 7.
Salts of weak acid and strong base e.g.,CH3COONa are basic in nature.
Salts of strong acid and weak base e.g.,NH4Cl, are acidic
Salts of weak acid and weak base, e.g.,CH3COONH4. The pH is determined by
the formula pH = 7 + ½ (pKa – pKb)
Solubility product- product of the molar concentrations of the ions in a
saturated solution, each concentration term raised to the power equal to the no.
of ions produced.
ONE MARK QUESTIONS
Q.1. Mention the factors that affect equilibrium constant.
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