CAHPTER NO 6

                              CHAPTER NO 6

     CHEMICAL EQUILIBRIUM

*IRREVERSIBLE  REACTIONS

A reaction which proceeds in a definite direction till its completion is known as irreversible reactions

                        Or

The reaction in which reactants are completely converted into products is known as irreversible reactions

→ this reaction is also known as (one way reaction) (complete reaction) (uni-directional)

EXAMPLE

1)  AgNO₃ + Nacl  → AgCl + NaNO₃

2)  C + O₂  → CO₂

REPRESENTATION

It is denoted by single arrow (→)

*REVERSIBLE  REACTIONS

Reactions in which reactants are partially converted into products are known as reversible reactions

                              Or

A reaction in which reactants forms product and after some time products are converted into reactants and an equilibrium is establish is known as reversible reactions

→ this reaction is also known as (incomplete reactions) (two way reaction)(bi-directional)

EXAMPLE

1     1)   H₂  + I₂ <==>  2HI

2     2)   N₂ +3H₃ <==>NH₃

REPRESENTATION

It is denoted by double arrow (<==>)

                                

*FORWARD REACTION

Chemical reaction in reversible reaction which take place in forward direction is known as forward reaction

                       OR

The reaction which proceed from reactants to product side is known as forward reaction

EXAMPLE

H₂  + I₂ <==>  2HI

In this reaction  ( H₂  + I₂  →     2HI ) is a forward reaction.

*BACKWARD REACTION

Chemical reaction in reversible reaction which take place in backward direction is known as backward reaction

                     OR

The reaction which proceed from product to reactants side in known as backward reaction

EXAMPLE

  H₂  + I₂ <==>  2HI

In this case (2HI  →  H₂  +  I₂ ) is a backward reaction 

*backward reactions are also known as reverse reaction.

*EQUILIBRIUM

When forward reaction and backward reaction occur at same rate the then that time is called the time of equilibrium.

                                             OR

A time when the rate of forward reaction is equal to the rate of backward reaction is known as state of equilibrium or chemical equilibrium

GRAPH

A <==> B

When the reaction begins reactants “A” starts converting into product “B” its mean concentration of “A” decreases by the passage of time and the concentration of “B” increases than at time “t” equilibrium will establish (which is called the time is called the time of equilibrium ) and the line of the graph will be straight

*CONCENTRATION (Active mass)

The amount (quantity) of a chemical substance is called as concentration

                                    OR

The amount of solute in given amount of solution is called as its concentration

                                    OR

The ratio of no of moles and volume is called concentration

REPRESENTATION

It is denoted by square brackets [ ]

UNIT

Moles/dm³                                                                                        

                                                                                                        -: 1dm³=1litre 

LAW OF MASS ACTION  (Rate Law)

This law was given by guldberge and wage  in 1864

  “The rate at which a substance reacts is directly proportional to its active mass (concentration) and the rate of reaction is directly proportional to the products of concentration of its reactants”

EXPLANATION ( IN URDU ) 

Reaction ki raftaar reactant ki concentration py depend hai aur agar aik sy ziada reactants hon to products banny ki raftaar reactants k product yani (multiplication) py depend hgi.  

Matlab ye k jitni ziada reactants ki concentration hgi products banny ki speed ya raftaar utni hi ziada hgi..

Now considering a general reaction.

A + B  →  C + D

Applying law of mass action

Rate of reaction  ∝  [A].[B]

dx/dt = k [A].[B]  -: it s also known as rate expression

-: k = rate constant

-: dx = change in concentration

-: dt = change in time

DERIVATION OF KC

Considering a reaction

XA + YB <==> aC + bD

Rate of forward reaction  ∝ [A]^X [B]^Y

   rf = k₁ [A]^X [B]^Y

Rate of backward reaction  ∝  [C]^a [D]^b

   rf = k₂ [C]^a [D]^b

     at equilibrium

          rate of forward reaction = rate of of backward reaction

                        k₁ [A]^X [B]^Y = k₂ [C]^a [D]^b

                         K₁ / K₂ =[C]^a [D]^b /[A]^X [B]^Y

                        -: K₁ / K_{2  =} constant => kc (equilibrium constant)

                         kc =[C]^a [D]^b /[A]^X [B]^Y

                                       kc  = [products]/[reactants]

EQULIBRIUM CONSTANT

    It is a ratio of concentration of products to the concentration of reactants

EXAMPLE

      H₂  + I₂ <==>  2HI

-: kc = [products]/[reactants]

   kc = [H₂].[I₂]/[HI]²

  PREPARED BY :  SAQIB NAEEM AWAN