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Showing posts with label CHEMICAL EQUILIBRIUM:. Show all posts
Showing posts with label CHEMICAL EQUILIBRIUM:. Show all posts

Saturday, September 2, 2023

Gibb's free energy (∆G) and Equilibrium constant (Kc):

The part f energy which is converted into usefull work called Gibb's free energy or Gibb's function.
 
Energy (H) = Useful work (G) + Non useful (TS)

We van not calculate absolute value of 'G' so we calculate change in Gibb's free energy. 

             ∆G = ∆H -∆TS
       ∆G = ∆H - (∆TS + T∆S). ......(1)

Standard Gibb's energy (∆G°) change at  standard condition is 1 bar  and 298 K

             ∆G° = ∆H° -∆TS°  .......(2) 

Relation between ∆G° and Equilibrium constant (K):




Factor's Affecting Equilibrium Constant

(1) Le-Chetelier'e principle
(i) Effect of change in  temperature
(ii) Effect of change in  concentration 
(iii) Effect of change of volume of container at equilibrium
(iv) Effect of change in pressure
(v) Effect of Catalyst at equilibrium
(vi) Effect of Addition of Inert gas
(a) At constant volume
(b) At constant pressure 

          [End of Chapter = ∆∆∆]

Application of Equilibrium Constant (K):

(1) Predicting extent of reactions
(2) Predicting of stability of reactants and products
(3) Predicting direction of reactions at any instant of reaction (Qc)
(4) Predicting concentration of reactants and products at equilibrium.
(5) Degree of dissociation and Kp and Kc in term of DOD.
(6) Degree of dissociation and Vapour density.

Tuesday, August 29, 2023

Relation between Kp and Kc and Law of Mass of action: Equilibrium constants:

LAW OF MASS ACTION: Law of mass action is applicable for only reversible chemical reactions and it is an imperial law.

The law state that “ At a fixed temperature the rate of a chemical reaction is directly proportional to the product of reactive mass of reactants raised to the their respective Stoichiometric coefficients ” The law of mass action is by Guldberg and Waage.

(1) Equilibrium Constants in term of concentration ( KC):
At the constant temperature, let us consider the following reversible reaction
According to law of mass action - The rate of forward reaction
The rate of reverse reaction-
Where Kf and Kb  is the rate constant of the forward reaction and backward reaction respectively
We know at equilibrium, the two rates of forward as well as backward are equal. ie
Rate of reaction = Rate of forward reaction – Rate of backward reaction = 0
Kc=Kf/Kb
Unit of Kc= (Conc)ng
(2) Equilibrium Constants in term of Pressure( Kp):
Consider the general chemical  reaction taking place at constant temperature.
From law of mass action- rate forward reaction is directly proportional  to product of active mass of reactants and rate backward reaction is directly proportional  to product of active mass of products.

For an ideal gas PV=nRT

Where 

P= Pressure in atm

V=Volume in liters

n=Number of gaseous moles

R=Gas constant  

  =  0.0821 L atm/mol/K or 1/12 L atm /mole/K

T=Temperature in kelvin

                                      = total number of moles of gaseous products -total number of moles of gaseous reactants

Illustrated examples:

The chemical equilibrium constant Kc for the decomposition of PCl5 is 0.0625 mole L^-1 at 300^C. What will be the value of Kp is ?

 

The value of Kc for the reaction (formation of ammonia by haber process) is 0.50 at 400º C.What will be the value of Kp at 400ºC when concentration are expressed in mole litre.1 and pressure in atmosphere ?



SOLUTION: 

For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) The Kp is 4.3 × 10^-4 at 375°C. Calculate Kc for the reaction. ?

SOLUTION:

Methanol (CH3OH) is manufactured industrially by the reaction CO(g) + 2H2(g) ⇌ CH3OH(g) The equilibrium constant (Kc) for the reaction is 10.5 at 220°C. What is the value of Kp at this temperature ?

 SOLUTION: Give Data ,Kc = 10.5 ,T= 220oC = (220 + 273)K = 493 K

At 700 K, the equilibrium constant Kp, for the reaction, dissociation of Sulphur trioxide to Sulphur dioxide is 1.8 × 10^3 kPa What is the numerical value of Kc for this reaction at the same temperature



SOLUTION:

Relation Between vapour density and degree of dissociation : Theory and Numericals:

 

(1) Ammonium carbamate when heated to 200 °C gives a mixture of NH3​ and CO2​ vapour with a density of 13. What is the degree of dissociation of ammonium carbamate?







Ammonium carbamate when heated to 200 °C gives a mixture of NH3​ and CO2​ vapour with a density of 13. What is the degree of dissociation of ammonium carbamate?

The observed molecular weight of N 2​O4​ is 80 g mol^−1 at 350 K. The percentage of dissociation of N2​O4​ (g) at 350 K is ?