Important Short notes and questions of Chemical and Ionic Equilibrium

  *What is Equilibrium?* 

Equilibrium is the state of a process in which the properties like temperature, pressure, and concentration etc of the system do not show any change with passage of time.

➖In all processes which attain equilibrium, two opposing processes are involved.

➖Equilibrium is attained when the rates of the two opposing processes become equal. 

➖If the opposing processes involve only physical changes, the equilibrium is called Physical Equilibrium. 

 *Types of Physical Equilibrium* 

➖Solid – liquid Equilibrium: H2O(s) = H2O(l) 

➖Liquid – Gas Equilibrium: H2O(l) = H2O(g)

➖Solid – Solution Equilibrium: Salt(Solid) = Salt(in solution)

➖Gas –Solution equilibrium: CO2(g) = CO2(in solution)

 

What is Reversible reaction? 

A reaction in which not only the reactants react to form the products under certain conditions but also the products react to form reactants under the same conditions 

Examples: 

3Fe(s) + 4H2O(g) --> Fe3O4(s) + 4H2(g)

 *What are Irreversible reaction?* 

A reaction cannot take place in the reverse direction, i.e. the products formed do not react to give back the reactants under the same condition.

 *How to identify irreversible reaction?* 

Example: 

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(g)

 In Above example, AgCl precipitated so, it can't participate in reaction with NaNO3

 

*CHEMICAL EQUILIBRIUM:* 

If the opposing processes are chemical reactions, the equilibrium is called Chemical Equilibrium. 

Characteristics of Equilibrium State

It can be attained only if the reversible reaction is carried out in closed vessel.

It can be attained from either side of the reaction.

 *Role/Effect of Catalyst on Equilibrium* 

A catalyst can hasten the approach of equilibrium but does not alter the state of equilibrium.

It is dynamic in nature i.e. reaction does not stop but both forward and backward reactions take place at equal rate.

Change of pressure, concentration or temperature favours one of the reactions (forward or backward) resulting in shift of equilibrium point in one direction.

Law of Mass Action:

“The rate at which a substance reacts is directly proportional to its active mass and rate of a chemical reaction is directly proportional to product of active masses of reactants each raised to a power equal to corresponding stoichiometric coefficient appearing in the balanced chemical equation”.

For reaction 

aA + bB <=> cC + dD

Rate of forward reaction(Rf) ∝ [A]^a*[B]^b

Hence rate of forward reaction(Rf) =  K[A]^a*[B]^b

where Kf is specific rate of reaction  or  rate constant or velocity constant of forward reaction at that temperature.

rate of backward reaction(Rb) ∝ [C]^c*[D]^d

Hence rate of backward reaction(Rb) =  Kb[C]^c*[D]^d

where Kb is specific rate of reaction or  rate constant or velocity constant of the backward reaction at that temperature.

At Equilibrium,

Rate of Forward reaction(Rf) = Rate of Backward reaction(Rb)

Equilibrium Constant:

Kc= Kf/Kb =

{[C]^c*[D]^d}/{[A]^a*[B]^b}

 *How to find Weather precipitation takes place or not if Solubility product known.* 

Qsp (Ionic Product)  

a) Product of ionic concentration due to ions already present in water or from a salt.

b) Qsp (Ionic Product). may be and may not be equal to Ksp. 

c) If Qsp (Ionic Product) > Ksp ; precipitation takes place till I.P. equals Ksp

d) If Qsp (Ionic Product)< Ksp ; a precipitate will not be formed and the solution will be unsaturated.

e) If Qsp (Ionic Product)= Ksp ; a precipitate will not form an the solution is saturated in that salt.

Thermodynamic relationship between Equilibrium and Gibbs Free energy:

(a) The catalyst never affects ∆Gº of the reaction at equilibrium.

(b) (i) If ∆G° = 0, then Kc

 = 1. 

(ii) If ∆G° > 0,(+ ve), then Kc

 < 1. So, reverse reaction is possible, i.e., less concentration of products of 

equilibrium state. 

(iii) If ∆G° < 0, (– ve), then Kc

 > 1. 

So, forward reaction is possible where a large concentration of products is observed till the point of 

equilibrium is attained.

(c) A negative ΔG° never indicates the complete transformation of the reactants into products. Similarly, a positive ΔG° does not indicate the absence of product formation.

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