Application Of Le-Chatelier's Principle
Category : JEE Main & Advanced
The Le-Chateliers principle has a great significance for the chemical, physical systems and in every day life in a state of equilibrium.
(1) Applications to the chemical equilibrium
(i) Synthesis of ammonia (Haber’s process)
\[\underset{1\ vol}{\mathop{{{N}_{2}}}}\,+\underset{3\ vol}{\mathop{3{{H}_{2}}}}\,\] \[\rightleftharpoons \] \[\underset{2\ vol}{\mathop{2N{{H}_{3}}}}\,+23kcal\] (exothermic)
(a) High pressure \[(\Delta n<0)\]
(b) Low temperature
(c) Excess of \[{{N}_{2}}\] and \[{{H}_{2}}\]
(d) Removal of \[N{{H}_{3}}\] favours forward reaction.
(ii) Formation of sulphur trioxide
\[\underset{2\ vol}{\mathop{2S{{O}_{2}}}}\,+\underset{1\ vol}{\mathop{{{O}_{2}}}}\,\] \[\rightleftharpoons \] \[\underset{2\ vol}{\mathop{2S{{O}_{3}}}}\,+45\ kcal\] (exothermic)
(b) Low temperature
(c) Excess of \[S{{O}_{2}}\] and \[{{O}_{2}}\], favours the reaction in forward direction.
(iii) Synthesis of nitric oxide
\[\underset{1\ vol}{\mathop{{{N}_{2}}}}\,+\underset{1\ vol}{\mathop{{{O}_{2}}}}\,\] \[\rightleftharpoons \] \[\underset{2\ vol}{\mathop{2N{{O}_{{}}}}}\,-43.2\ kcal\] (endothermic )
(a) High temperature
(b) Excess of \[{{N}_{2}}\] and \[{{O}_{2}}\]
(c) Since reaction takes place without change in volume i.e., \[\Delta n=0\], pressure has no effect on equilibrium.
(iv) Formation of nitrogen dioxide
\[\underset{2\ vol}{\mathop{2N{{O}_{{}}}}}\,+\underset{1\ vol}{\mathop{{{O}_{2}}}}\,\] \[\rightleftharpoons \] \[\underset{2\ vol}{\mathop{2N{{O}_{2}}}}\,+27.8\ Kcal\]
(c) Excess of \[NO\] and \[{{O}_{2}}\] favours the reaction in forward direction.
(v) Dissociation of phosphours pentachloride
\[\underset{1\ vol}{\mathop{PC{{l}_{5}}}}\,\] \[\rightleftharpoons \] \[\underset{1\ vol}{\mathop{PC{{l}_{3}}}}\,+\underset{1\ vol}{\mathop{C{{l}_{2}}}}\,-15\ kcal\]
(a) Low pressure or high volume of the container, \[\Delta n>0\] (b) High temperature (c) Excess of \[PC{{l}_{5}}\].
(2) Applications to the physical equilibrium
(i) Melting of ice (Ice – water system)
\[\underset{\text{(Greater}\ \text{Volume)}}{\mathop{\text{Ice}}}\,\] \[\rightleftharpoons \] \[\underset{\text{(Lesser}\ \text{Volume)}}{\mathop{\text{Water}}}\,-x\ kcal\]
(In this reaction volume is decreased from 1.09 c.c. to 1.01 c.c. per gm.)
(a) At high temperature more water is formed as it absorbs heat.
(b) At high pressure more water is formed as it is accompanied by decrease in volume.
(c) At higher pressure, melting point of ice is lowered, while boiling point of water is increased.
(ii) Melting of sulphur : \[{{S}_{(s)}}\] \[\rightleftharpoons \] \[{{S}_{(l)}}-x\ kcal\]
(This reaction accompanies increase in volume.)
(a) At high temperature, more liquid sulphur is formed.
(b) At higher pressure, less sulphur will melt as melting increases volume.
(c) At higher pressure, melting point of sulphur is increased.
(iii) Boiling of water (water- water vapour system) \[\underset{\text{(Low}\ \text{volume)}}{\mathop{\text{Water}}}\,\]\[\rightleftharpoons \]\[\underset{\text{(Higher}\ \text{volume)}}{\mathop{\text{Water}\ \text{Vapours}}}\,-x\ kcal\]
(It is accompanied by absorption of heat and increase in volume.)
(a) At high temperature more vapours are formed.
(b) At higher pressure, vapours will be converted to liquid as it decreases volume.
(c) At higher pressure, boiling point of water is increased (principle of pressure cooker).
(iv) Solubility of salts : If solubility of a salt is accompanied by absorption of heat, its solubility increases with rise in temperature; e.g., \[N{{H}_{4}}Cl,\ {{K}_{2}}S{{O}_{4}},\ KN{{O}_{3}}\] etc.
\[KN{{O}_{3(s)}}+(aq)\xrightarrow{{}}KN{{O}_{3(aq)}}-x\ kcal\]
On the other hand if it is accompanied by evolution of heat, solubility decreases with increase in temperature; e.g., \[CaC{{l}_{2}},\] \[Ca{{(OH)}_{2}},NaOH,\ KOH\]etc.
\[Ca{{(OH)}_{2(\ s)}}+(aq)\xrightarrow{{}}Ca{{(OH)}_{2\ (aq)}}+x\ kcal\]
You need to login to perform this action.
You will be redirected in
3 sec
