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Class notes chemistry Chemistry Simplified NCERT Class 11
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Class notes chemistry Chemistry Simplified NCERT Class 11
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UNIT 7 EQUILIBRIUMCHEMICAL EQUILIBRIUM
PHYSICAL EQUILIBRIUM
Equilibrium involving only physical changes is called physical equilibrium.
Eg:- Solid Liquid , Liquid Gas , Solid Vapour
GENERAL CHARACTERISTICS OF PHYSICAL EQUILIBRIUM
Equilibrium can be established only in case of closed system.
The equilibrium is always dynamic in nature.
The measurable properties of the system become constant at equilibrium.
At equilibrium, there exists an expression involving the concentration of reacting
substances which become constant at a given temperature.
HENRY’S LAW
The law states that at a constant temperature, the solubility of a gas in a liquid is
directly proportional to the pressure of the gas.
OR
Henry’s law states that, the solubility of a gas is proportional to the pressure.
Eg:- In soda water bottles, the dissolved and un dissolved molecules of CO 2 exist in
equilibrium.
When the bottle is opened, the CO2 dissolved in it escapes out rapidly with a fizz.
This fizzing out of soda bottle can be easily understood in terms of Henry’s law.
REVERSIBLE REACTIONS
Reactions in which the products of the reaction can react with one another under
suitable conditions to give back the original reactants.
Eg:- N2 3H2 2NH3
2SO2 O2 2SO3
2HI H2 I2
IRREVERSIBLE REACTIONS
Reactions in which the products of the reaction do not react back to give the
reactants.
HCl NaOH NaCl H2O
Eg:
AgNO3 NaCl AgCl NaNO3
CHEMICAL EQUILIBRIUM
The state of reversible reaction at which the rate of forward reaction is equal to the
PREPARED BY HAIZEL G. ROY, HSST (HG) CHEMISTRY, GOVT. H.S.S. KALAMASSERY, ERNAKULAM Page | 1
, rate of backward reaction and the composition of the system remains constant.
CHEMICAL EQUILIBRIUM IS DYNAMIC IN NATURE
In a chemical reaction, both forward and backward reactions do not stop but
proceed at equal rates.
The concentration of reactants and products remain constant.
Therefore, the equilibrium is called dynamic equilibrium.
CHARACTERISTICS OF CHEMICAL EQUILIBRIUM
Chemical equilibrium is dynamic in nature.
The observable properties of the system become constant at equilibrium and remain
unchanged.
The equilibrium can be approached from either direction.
The equilibrium can be attained only if the system is a closed one.
A catalyst cannot alter the position of equilibrium.
The free energy change at constant temperature and pressure is zero.
LAW OF MASS ACTION
The law states that, “the rate of a reaction is directly proportional to the product of
the molar concentrations of the reacting substances at constant temperature”.
Consider a reaction A B Pr oducts .
According to law of mass action,
Rate of the reaction, r α [A][B]
r = K[A][B]
where [A] and [B] are the molar concentrations of the reactants A and B
respectively.
K is a constant known as rate constant.
RATE CONSTANT
According to law of mass action, r = K[A][B]
If the concentration of each of the reactants is unity,
i.e., [A] = [B] = 1, then r = K.
The rate constant of a reaction at a given temperature may be defined as the rate
of the reaction when the concentration of each of the reactants is unity.
EQUILIBRIUM CONSTANT
Consider a general reversible reaction, aA bB cC dD
According to law of mass action, the rate of the forward reaction is given as
rf [A]a[B]b
PREPARED BY HAIZEL G. ROY, HSST (HG) CHEMISTRY, GOVT. H.S.S. KALAMASSERY, ERNAKULAM Page | 2
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