ARRHENIUS ACID-BASE CONCEPT

CHARACTERS OF ACIDS:
(1) acids convert blue litmus to red and methyl orange  indicator to  red .
(2) Sour in taste.
(3) It liberate hydrogen gas with active metals.
(4) Acids neutralised the effect of base 
(5) acids increases the conduction of water.
CHARACTERS OF BASES:
(1) bases convert the red litmus to blue and methyl orange indicator to yellow.
(2) Phenylphthlene indicator (white) to pink.
(3) Bitter in taste and soapy in touch.
(4) Bases neutralised the effect of acid.
(5) They increases conductance of water.
ACID BASE CONCEPT:
(1) ARRHENIUS ACID-BASE CONCEPT
(2) BRONSTED LOWERY ACID-BASE CONCEPT 
(3) LEWIS ACID-BASE CONCEPT

(1) ARRHENIUS ACID-BASE CONCEPT
the substance which produces H+ in aqueous solution is consider as acid and the substance which give produces OH- in aqueous solution is consider as base
Arrhenius theory depend upon dissociation of water.

Type of Arrhenius acids:

Type of Arrhenius Bases :

         

Feature of Arrhenius theory:

(1) OH¯ ion is present also in hydrated form of H₃O₂¯, H₇O₄¯, H₅O₃¯

      H⁺ ion is present also in hydrated form of H₃O⁺, H₅O₂⁺, H₇O₃+, H₉O₄⁺

(2) Neutralisation reaction can be easily explain by the Arrhenius theory .acids furnishing H⁺ ion  in water to large extent are strong acid.

Strength of acid or base:

(3) If Ka increases then concentration of H⁺ increases hence acidic strength is increases.

Similarly the base furnishing OH^- ions to the large extent are strong base

Kb is dissociation constant for bases, if Kb is increases OH- increases, hence basic strength of base

(4)The term strong is used only for those acids or bases or bases which dissolved almost completely in water.

LIMITATIONS OF ARRHENIUS THEORY

(1) This theory explain nature of a substance only aqueous medium . It cannot be applied for non aqueous solution.
(2) It could not explain formation of hydronium ions like H₃O- , H₅O₂- , and H₇O₃- .
(3) the nature of aqueous solution of AlCl₃, CuSO₄ ,BF₃, B(OH)₃ etc are acidic and aqueous solution of NH₃ ,NaCO₃ ,RNH₂ R2NH,  R₃N , _C2H5N  etc are basic in nature cannot be explain by Arrhenius Concept.
(4) there are many  Amphoteric hydroxide Zn(OH)₂  Al(OH)₃ ,Pb(OH)₂ , which cannot be  explain  by Arrhenius Concept.
(5) Arrhenius explain only when H⁺ is released it cannot explain when H+ is taken.

                                                 

SPONTANEOUS AND NON SPONTANEOUS PROCESS

SPONTANEOUS PROCESS: Those process which have natural tendency to take place ,they may or may not require initiation.
For example
(1) Flow of water from higher level to lower level .
(2) Flow of heat from high temperature to lower temperature.
(3) Radioactivity
(4) Cooling of cup of tea .
(5) Evaporation
(6) Condensation 
(7) Sublimation
(8) Burning of candle
(9) Dissolution of salt and sugar in water
(10) Burning of fuel
(11) melting of ice at room temperature.
NON SPONTANEOUS PROCESS: All spontaneous processes are non spontaneous processes in reverse direction it requires spot of external energy for their progress.
CRITERIA FOR SPONTANEITY:
(1) If dS universe is greater than Zero  then process is spontaneous (reversible)
(2) If dS is Zero then process is in reversible state of equilibrium
(3) If dS is lower than Zero then  process is non spontaneous
For  a spontaneous process entropy of univers is greater than Zero . In order to use entropy has a sole criteria , we need to have information about system as well as surrounding.
dS(system) + dS(surr) is greater than  Zero
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In order to explain the spontaneous behaviour by using the parameters of system we can established  two criteria.
(1) Randomness
(2) Criteria of energy
A spontaneous process is one in which energy ( enthalpy) decreasing and Randomness of system increasing.
For spontaneous proceDH=-ve and dS=+ve