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Session : CHEMICAL EQUILIBRIUM - 1 Session
Syllabus : Syllabus Equilibrium in physical processes,
Dynamic nature of equilibrium,
Law of mass action,
Equilibrium constant
Types of Equilibria
Relation between Kp and Kc
Computation of Equilibrium Constant
Introduction to Chemical Equilibrium : Introduction to Chemical Equilibrium Why do we study chemical equilibrium To answer : “ To what extent reactants will convert to products”
The answer is linked to “ How far does a reaction proceed towards completion before it reaches a state of chemical equilibrium ? ” What do we mean by state of equilibrium State where concentration of reactants and product no longer change Does it mean reaction stops ? Rates of forward and backward reactions are same Rate at which reactants is changing to products is same as products changing to reactants Dynamic Equilibrium
Equilibrium in Phase Changes : Equilibrium in Phase Changes At equilibrium:
Rate of melting = Rate of freezing Dynamic Equilibrium is observed in phase transformation processes However , intense activity at the boundary of ice and water Freezing Point / Melting point of a substance :
For pressure condition of 1 atm , the temperature at which solid and liquid phase of a pure substance are at equilibrium
Equilibrium in Phase Changes : Equilibrium in Phase Changes At equilibrium: Rate of evaporation = Rate of condensation Molecules with higher molecule at the liquid surface escape - Evaporation The molecules in vapour phase keep on increasing leading to increase in pressure Low molecular speed molecules in vapour phase also condensing back to liquid phase At equilibrium and constant temperature , the pressure exerted by molecules in vapour phase is - Vapour pressure of liquid Will there be equilibrium , if container was open
Vapour Pressure and Boiling : Vapour Pressure and Boiling At equilibrium and constant temperature , the pressure exerted by molecules in vapour phase is - Vapour pressure of liquid The temperature, at which vapour pressure becomes equal to external atmospheric pressure , is called Boiling Point of liquid At a given temp. , different liquids have different vapour pressure , as intermolecular forces are different At 273 K , water - 610 Pa , ethanol -
Equilibrium in Phase Changes : Equilibrium in Phase Changes At equilibrium:
Rate of sublimation = Rate of deposition
Equilibrium in dissolution of solids : Equilibrium in dissolution of solids At equilibrium: Rate of dissolution = Rate of crystallisation Solids in Liquids Gases in Liquids CO2 coming out when soda water bottle is opened Governed by Henry’s Law
Common Characteristics of Physical Equilibria : Common Characteristics of Physical Equilibria Possible only in a closed system at a given temperature.
The opposing processes occur at the same rate and there is a dynamic but stable condition.
Equilibrium is characterised by constant value of one of its parameters at a given temperature. ( e.g. vapour pressure ) The magnitude of these quantities at any stage indicates the extent to which the reaction has proceeded before reaching equilibrium
Equilibrium in Chemical Process : Equilibrium in Chemical Process In chemical reactions , the equilibrium is the state of reaction at which concentration of reactants and products remain constant over a period of time Rate of forward reaction (from left to right ,i.e., N2 and H2 combining to form Ammonia) = Rate of reverse reaction ( Ammonia dissociating in to N2 and H2 ) Will reaction stop at equilibrium
Equilibrium in Chemical Process : Equilibrium in Chemical Process In chemical reactions , the equilibrium is the state of reaction at which concentration of reactants and products remain constant over a period of time At equilibrium, rate of decomposition of N2O4 = rate of combination of NO2 Increase in [NO2] starts declining as NO2 starts combining to form N2O4 (Reverse reaction)
Equilibrium in Chemical Process : Equilibrium in Chemical Process At equilibrium, rate of combination of NO2=rate of decomposition of N2O4 Same equilibrium state is achieved as
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Characteristics of Chemical Equilibrium : Characteristics of Chemical Equilibrium At Equilibrium ,
Concentration of reactants and products becomes constant
Rate of forward reaction = Rate of backward reaction
At equilibrium the free energy changes of the system is equal to zero Chemical equilibrium can be attained from either direction, i.e., from the direction of the reactants as well as from the direction of products.
Law of Chemical Equilibrium ( Law of Mass Action) : Law of Chemical Equilibrium ( Law of Mass Action) What will be the concentration of reactants and products at equilibrium ? How composition can be altered ? “ To what extent reactants will convert to products” At equilibrium, concentrations are related by the following relations
Law of Chemical Equilibrium ( Law of Mass Action) : Law of Chemical Equilibrium ( Law of Mass Action) Law of Chemical Equilibrium :
At a given temperature,
The product of concentrations of the reaction products raised to the respective stoichiometric coefficient in the balanced chemical equation divided by
The product of concentrations of the reactants raised to their individual stoichiometric coefficients has a constant value. At equilibrium, concentrations are related by the following relations
Illustrative Problem : Illustrative Problem Solution :
Illustrative Problem : Illustrative Problem Calculate the equilibrium constant for the reaction If the equilibrium constant at 1395 K for the following are:
Illustrative Problem : Illustrative Problem
Illustrative Problem : Illustrative Problem At eqm. 0.4 0.13 0.7conc. Hence, answer is (b). Solution :
Equilibria in gas-phase reactions(Kp) : Equilibria in gas-phase reactions(Kp) Gaseous System : However , for gases pressure can be easily measured
Equilibria in gas-phase reactions(Kp) : Equilibria in gas-phase reactions(Kp)
Heterogeneous Equilibria : Heterogeneous Equilibria Molar Concn of pure solid and pure liquid is constant Concentration of pure solids and liquids is to be ignored while writing an equilibrium equation
Illustrative Problem : Illustrative Problem Solution :
Illustrative Problem : Illustrative Problem = 4.636 × 10–4 atm–2 Solution :
Computation of Equilibrium Concentrations : Computation of Equilibrium Concentrations Step 3 : Substitute eq. Concn in equilibrium equation Step 4 : Solve and find eq. Concn
Computation of Equilibrium Concentrations : Computation of Equilibrium Concentrations
Illustrative Problem : Illustrative Problem Step 3 : Substitute eq. Concn in equilibrium equation Step 4 : Solve and find eq. Concn Solution :
Solution Cont. : Solution Cont.
Illustrative Problem : Illustrative Problem Solution :
Solution Cont. : Solution Cont.
Illustrative Problem : Illustrative Problem Assume 1 mole of N2O4 initially Solution :
Illustrative Problem : Illustrative Problem 60 ml of H2 and 42 ml of I2 are heated in a closed vessel. At equilibrium the vessel contains 28 ml of HI. Calculate percentage of dissociation of HI. Solution :
Solution Cont. : Solution Cont. 60 ml of H2 and 42 ml of I2 are heated in a closed vessel. At equilibrium the vessel contains 28 ml of HI. Calculate percentage of dissociation of HI.