EQUILIBRIUM:-It is a state in reversible process when the rate of forward direction becomes equal to the rate of backward direction.
REVERSIBLE REACTION:It is a chemical reaction which can take place in forward as well as in backward direction. It is shown by using two half arrows in opposite direction(⇌). These reactions occur in a closed vessel.
EQUILIBRIUM:TYPES
1) PHYSICAL EQULIBRIUM
When the equilibrium state is reached in the physical processes it is called physical equilibrium . For example evaporation of water in a closed container Dissolution of a gas in a liquid under pressure in a closed vessel.
Q:-Give an example of gas liquid equilibrium from daily life?
Ans :- closed bottle of soda water.
2) CHEMICAL EQUILIBRIUM
When the equilibrium state is reached in a reversible chemical reaction it is called chemical equilibrium . For example the reaction between nitrogen and hydrogen to from ammonia.
CHARACTERISTICS:PHY EQUILIBRIUM
1) the measureable properties like temperature are pressure become constant at equilibrium state of a physical process.
2) equilibrium can be established only in closed systems.
3)the equilibrium state is always dynamic in nature not static.
4) at equilibrium sate concentrations of the different substances become constant.
5) the magnitude of equilibrium constant represents the extent to which the process proceeds before equilibrium is attained.
HENRY'S LAW
Q: - State and explain Henry’s law.
Ans: - This law states that at constant temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid surface. If S is the solubility of the gas then:
Sgas ∝ Pgas
Sgas = KH × Pgas
Here S is the solubility of the gas in mol/litre P is the partial pressure of the gas in atm. Here KH is Henry’s constant. It depends upon nature of gas, nature of liquid and temperature.
DALTON'S LAW
This law states that the total pressure of a mixture of non-reacting gases is equal to the sum of their partial pressures. For example if PA,PB and PC are the partial pressures of gases A,B, and C respectively then the total pressure will be given by:
Q:What is partial pressure ?
Ans:the pressure that each gas would exert if present alone in the same amount,in the same vessel at the same temperature as that of the gaseous mixture.
CHARACTERISTICS OF CHEMICAL EQUILIBRIUM
1) at equilibrium state concentrations of reactants and products become constant.
2) at equilibrium state the rate of forward reaction becomes equal to the rate of backward reaction.
3) a chemical equilibrium can be established only in the closed system
4) a chemical equilibrium is dynamic in nature and not static.
5) chemical equilibrium can be attained in either direction .
6) a catalyst does not disturb the state of chemical equilibrium.
CONCENTRATION
It is the number of moles of substance dissolved per litre of the solution.it is also called active mass. It is written by enclosing the formula of a compound in the square brackets. E.g. [NaOH].
UNITS: - mol ⁄ lit
REACTION RATE
The rate of change of concentration of reactants or products per unit time is called rate of reaction.
Consider a general reaction.
R → P
Rate = -Δ[R]/Δt = Δ[P]/Δt
-Δ[R]/Δt = [final conc.]/final time ─ [initial conc.]/initial time
UNITS:- mol ⁄ lit ⁄ sec
LAW OF MASS ACTION
This law states that the rate of reaction is directly proportional to the product of molar concentrations of all the reactants. Consider following general reaction:
A + B → C
Rate α [A] × [B]
Rate = k × [A] × [B]
Here k is called rate constant
When [A] = 1; [B] = 1
Then Rate = k
Thus rate constant is defined as rate of reaction when concentration of each of the reactant is unity.
Q:State and Explain Law of Chemical Equilibrium
It states that in a chemical reaction at equilibrium the ratio of product of molar concentrations of the products to the product of molar concentrations of the reactants with each concentration term raised to a power equal to its stoichiometric coefficient in the balanced chemical equation is a constant at constant temperature and is known as equilibrium constant. For example consider a general reversible reaction:
A + B ⇌ C + D
At equilibrium state the equilibrium constant is given by :
KC = ([𝐶]×[𝐷])/([𝐴]×[𝐵])
The above mathematical equation is called law of chemical equilibrium
DERIVATION OF LAW
KC = ([𝐶]×[𝐷])/([𝐴]×[𝐵])
The above equation of law of chemical equilibrium can be derived using law of mass action to a reversible reaction in equilibrium: Consider the following general reversible reaction:
A + B ⇌ C + D
according to the law of mass action the rate of above reversible reaction in the forward direction will be given by:
Rf ∝ [A]×[B] ………………………(1)
Rf = Kf [A]×[B] …………………….(2)
Here Kf is called rate constant for the forward reaction. Similarly using law of mass action rate of backward reaction is given by:
Rb ∝ [C]×[D] ………………………(3)
Rb = Kb [C]×[D] …………………….(4)
Here Kb is the rate constant for the backward reaction. Now at equilibrium the rate of forward reaction will be equal to the rate of backward reaction :
Rf = Rb
By substituting the values of Rf 𝑎𝑛𝑑 Rb from equation 2 and 4 we get;
Kf [A]×[B] = Kb [C]×[D] ………………….(5)
rearrange equation 5 we get:
(𝐾𝑓)/𝐾𝑏=([𝐶]×[𝐷])/([𝐴]×[𝐷])………………………(6)
As Kf and Kb are constants hence their ratio is also constant :
(𝐾𝑓)/𝐾𝑏= KC
Hence by substituting the value of Kf /Kb the equaiton no (6) becomes :
KC=([𝐶]×[𝐷])/([𝐴]×[𝐵])
This mathematical equation is called law of chemical equilibrium.
CHEMICAL EQUILIBRIA:TYPES
HOMOGENEOUS EQUILIBRIUM
The equlibrium in which all the reactants and products have same phase is called homogeneous equilibrium.e.g. haber’s process
HETEROGENEOUS EQUILIBRIA
The equilibrium in which reactants and products are present in different phases is called heterogeneous equilibrium.
CaCO3(s) ⇌ CaO (s) + CO2 (g)
CHARACTERISTICS:Kc
1) The value of equilibrium constant is independent of the original concentrations of the reactants
2) Equilibrium constant is applicable only when the concentrations of the reactants and products have attained their equilibrium state.
3) Every reaction has definite value of equilibrium constant at a particular temperature.
4) Its value is not affected by the presence of catalyst in the reaction
5) Value of K for the forward reaction is inverse of the Kc for backward reaction.
e.g. H2 + I2 ⇌ 2HI
6) The value of Kc tells us about the extent to which a reaction proceeds in the forward or backward direction.
APPLICATIONS OF Kc
1) prediction of extent of reaction :-
it predicts the extent of completion of reaction as follow :-
a) if Kc > 1000 then the concentration of products will be greater than the reactants at equilibrium. It means reaction has undergone almost to completion.
b) if Kc < 0.001 then the concentration of reactants is much more than the products at equilibrium. It means reaction will proceed to a very small extent.
c) If the value of Kc ranges from 0.001 to 1000. it means concentrations of reactants and products are comparable.
Back Next
0 Comments