CHEMICAL EQUILIBRIUM

There are two types of chemical reactions on the basis of direction of reaction.

1)IRREVERSIBLE:-
They are one way reactions.Those reactions in which only reactants change in product are called irreversible reactions Or one way reactions.
Reactant ------> Product
EXAMPLE: C + O2 -----> CO2
This type of reactions complete in a definite time and are given by ionic and polar compounds.

REVERSIBLE REACTIONS:-
They are two reactions.Those reactions in which reactant change in to product and product change back in to reactants are called reversible reactions or two way reactions.

REPRESENTATION: Reversible reactions are represented by double arrow.
EXAMPLE: I2 + H2<====> 2HI
This type of reactions take place between covalent and non polar compounds and become complete.

FORWARD REACTION:-
Change of reactants into product is called forward reaction.

REVERSE REACTION OR BACKWARD REACTION:-
Change of product into reactant is called reverse reaction.

EQUILIBRIUM STATE OF REVERSIBLE REACTION:-
State of reversible reaction at which rate of forward reaction is equal to the rate of backward or reverse reaction is called equilibrium state.

EXPLANATION:-
When a reversible reaction starts, first forward reaction take place in which reactants chang into product then backward or reverse reaction start in which product change into reactants.After some time rate of forward and backward reaction become equal. This state of reaction is called equilibrium state. Mixture of reactants and products at equilibrium is called equilibrium mixture.At the equilibrium state concentration of reactants and product become constant and we can not observe any change in the amount of reactants and products with time, it look like reaction had became stop, but the reaction never stops.
Equilibrium of reaction is called dynamic equilibrium.

LAW OF MASS ACTION AND LAW OF EQUILIBRIUM:-
This law is given by Guild berg ang Waage in 1864.

DEFINITION:-
 Rate of chemical reaction is directly proportional to product of active mass and molar concentration of reactants.

REPRESENTATION OF ACTIVE MASS AND MOLAR CONCENTRATION:-
Active mass or molar concentration of reactants is represented by square bracket [] . Reactants are placed within the brackets and number of mole are given as exponents.
EXAMPLE: Active mass of 2H2 is represented as [H2]^2 and of 2NH3 is representes as [NH3]^2.

EXPRESSION OF EQUILIBRIUM CONSTANT Kc:-
Equilibrium constant is represented by Kc, when we take reactants and products in term of active mass or molar concentration.
Suppose m mole of a n moles of B reacts to give x moles of C and y moles of D by a reversible reaction.
mA + nB<===> xC + yD
According law of mass action:
Rate of forward reaction is directly proportional to [A]^m [B]^n
Or
Rate of forward reaction=k1[A]^m[B]^n where k1 is constant of forward reaction.
Rate of backward reaction is directly proportional to [C]^x[D]^y
Rate of backward reaction=k2[C]^x[D]^y where k2 is constant of backward reaction.

AT EQUILIBRIUM:-
Rate of forward reation is equal to rate of backward reaction.
By dividing above both equations we get Kc=[C]^x[D]^y/[A]^m[B]^n where kc is equilibrium constant it is equal to ratio of k1 to k2 or it is ratio of active mass or molar concentrtion of product and reactants at equilibrium.

EQUILIBRIUM CONSTABT Kp:-
It is for the gaseous reaction, when we take gasses in term of partial pressure instead of molar concebtration.

RELATIONSHIO BETWEEN Kc and Kp:-
There are three relations between Kp and Kc
.
1)Kp IS GREATOR THAN Kc:-
If reaction take place by increase of volume then Kp is greator than Kc or Kc is smaller than Kp.

2)Kp SMALLER THAN Kc:-
If reaction is take place by decrease in volume then Kp is smaller is than Kc or Kc is greator than Kp.

3)Kp IS EQUAL TO Kc:-
If the reaction takea place by smas volume then Kp is equal to Kc
.
APPLICATION OF LAW OF MASS ACTION:-
1)To predict the direction of reaction to acquire the equilibrium.
2)To determine extent of reaction.
1)TO PREDICT THE DIRECTION REACTION TO ACQUIRE THE EQUILIRIUM:-

We can predict the direction of reaction to acquire the equilibrium by comparing the ratio of initial concentration of products and reactants or K initial with equilibrium constant Kc.There are three cases.

Case:1 IF THE RATIO OF INITIAL CONCENTRAION (K initial) IS LESS THAN Kc:-
If K initial is less than Kc it means low product and more reactants are present than the equilibrium state, so the reaction take place in forward reaction, where some amount reactants changes to product then equilibrium state comes again.

Case:2 IF THE RATIO OF INITIAL CONCENTRATION (K initial) IS MORE THAN Kc:-
If K initial is more than Kc it means more product and less reactants are present than the equilibrium state, So the reaction take place in backward direction, where some amount of product changes to reactants and then equilibrium comes again.

Case:3 IF THE RATIO OF INITIAL CONCENTRATION(K initial) IS EQUAL TO Kc:-
If the K initial is equal to Kc it means reaction is at the equilibrium state, so the reaction take place equal in forward and backward direction.

2)TO PREDICT THE EXTENT OF REACTION UO TO EQUILIBRIUM:-
From the value of Kc for a reaction we can predict the extent of reaction upto equilibrium. There are three cases.
Case:1 Value of Kc is very high.
Casr:2 Value of Kc is very low.
Case:3 Value of Kc is intermediate