JEE Main & Advanced Chemistry Equilibrium / साम्यावस्था Types Of Equilibria

Types Of Equilibria

Category : JEE Main & Advanced


The equilibrium between different chemical species present in the same or different phases is called chemical equilibrium. There are two types of chemical equilibrium.

(1) Homogeneous equilibrium : The equilibrium reactions in which all the reactants and the products are in the same phase are called homogeneous equilibrium reactions.

\[{{C}_{2}}{{H}_{5}}OH\,(l)+C{{H}_{3}}COOH\,(l)\]? \[C{{H}_{3}}COO{{C}_{2}}{{H}_{5}}\,(l)+{{H}_{2}}O(l)\]

                           \[{{N}_{2}}\,(g)+3{{H}_{2}}\,(g)\] ? \[2N{{H}_{3}}(g)\]

               \[2S{{O}_{2}}\,(g)+{{O}_{2}}\,(g)\] ? \[2S{{O}_{3}}(g)\]

(2) Heterogeneous equilibrium : The equilibrium reactions in which the reactants and the products are present in different phases are called heterogeneous equilibrium reactions.

          \[2NaHC{{O}_{3}}\,(s)\]? \[N{{a}_{2}}C{{O}_{3}}\,(s)+C{{O}_{2}}\,(g)+{{H}_{2}}O\,(g)\]

\[Ca{{(OH)}_{2}}(s)+{{H}_{2}}O\,(l)\] ? \[C{{a}^{2+}}(aq)+2O{{H}^{-}}\,(aq)\]

                 \[CaC{{O}_{3}}\,(s)\] ? \[CaO\,(s)+C{{O}_{2}}\,(g)\]

                   \[{{H}_{2}}O\,(l)\] ? \[{{H}_{2}}O\,(g)\]


Homogeneous equilibria and equations for equilibrium constant (Equilibrium pressure is P atm in a V L flask)


\[\Delta n=0\,;\,\,{{K}_{p}}={{K}_{c}}\]

\[\Delta n<0\] ;  \[{{K}_{p}}<{{K}_{c}}\]

\[\Delta n>0;\ {{K}_{p}}>{{K}_{c}}\]


\[\underset{(g)}{\mathop{{{H}_{2}}}}\,\]+   \[\underset{(g)}{\mathop{{{I}_{2}}}}\,\]   ?     \[\underset{(g)}{\mathop{2HI}}\,\]

    \[\underset{(g)}{\mathop{{{N}_{2}}}}\,+\underset{(g)}{\mathop{3{{H}_{2}}}}\,\]? \[\underset{(g)}{\mathop{2N{{H}_{3}}}}\,\]



Initial mole

  1               1           0

    1          3              0

    2             1         0

   1              0        0

Mole at Equilibrium

(1–x)     (1– x)           2x

(1–x)      (3–3x)         2x

(2–2x)     (1–x)        2x

    (1–x)       x         x

Total mole at equilibrium


          (4 – 2x)         

              (3 – x)                             

                (1 + x)

Active masses

\[\left( \frac{1-x}{V} \right)\]  \[\left( \frac{1-x}{V} \right)\]   \[\frac{2x}{V}\]

\[\left( \frac{1-x}{V} \right)\] \[3\,\left( \frac{1-x}{V} \right)\] \[\left( \frac{2x}{V} \right)\]

\[\left( \frac{2-2x}{V} \right)\]  \[\left( \frac{1-x}{V} \right)\]   \[\left( \frac{2x}{V} \right)\]

\[\left( \frac{1-x}{V} \right)\]      \[\left( \frac{x}{V} \right)\]    \[\left( \frac{x}{V} \right)\]

Mole fraction

\[\left( \frac{1-x}{2} \right)\] \[\left( \frac{1-x}{2} \right)\]    \[\frac{2x}{2}\]

\[\frac{1-x}{2\,\left( 2-x \right)}\]\[\frac{3}{2}\left( \frac{1-x}{2-x} \right)\]\[\frac{x}{(2-x)}\]

\[\left( \frac{2-2x}{3-x} \right)\]     \[\left( \frac{1-x}{3-x} \right)\,\,\ \ \left( \frac{2x}{3-x} \right)\]

\[\left( \frac{1-x}{1+x} \right)\]  \[\left( \frac{x}{1+x} \right)\]  \[\left( \frac{x}{1+x} \right)\]

Partial pressure

\[p\,\left( \frac{1-x}{2} \right)\]\[p\,\left( \frac{1-x}{2} \right)\] \[p\,\left( \frac{2x}{2} \right)\]

\[P\left( \frac{1-x}{2(2-x)\_} \right)\,P\,\left( \frac{3(1-x)}{2(2-x)} \right)\,\frac{Px}{(2-x)}\]

\[P\,\left( \frac{2-2x}{3-x} \right)\]  \[P\left( \frac{1-x}{3-x} \right)\]  \[P\,\left( \frac{2x}{3-x} \right)\]

\[P\left( \frac{1-x}{1+x} \right)\] \[P\left( \frac{x}{1+x} \right)\]   \[P\left( \frac{x}{1+x} \right)\]



\[\frac{4{{x}^{2}}}{\left( 1-x \right){{\,}^{2}}}\]

\[\frac{4{{x}^{2}}{{V}^{2}}}{27\,\,\left( 1-x \right){{\,}^{4}}}\]

\[\frac{{{x}^{2}}V}{\left( 1-x \right){{\,}^{3}}}\]

\[\frac{{{x}^{2}}}{\left( 1-x \right)\,V}\]


\[\frac{4{{x}^{2}}}{\left( 1-x \right){{\,}^{2}}}\]

\[\frac{16{{x}^{2}}\,\left( 2-x \right){{\,}^{2}}}{27\left( 1-x \right){{\,}^{4}}{{P}^{2}}}\]

\[\frac{{{x}^{2}}\,\left( 3-x \right)\,}{P\,\left( 1-x \right){{\,}^{3}}}\]

\[\frac{P{{x}^{2}}}{\left( 1-{{x}^{2}} \right)\,}\]



Heterogeneous equilibria and equation for equilibrium constant (Equilibrium pressure is P atm)


\[N{{H}_{4}}HS(s)\]?\[N{{H}_{3}}(g)\] + \[{{H}_{2}}S(g)\]



Initial mole

     1                       0                0

    1        1                                  0

     1                                  0               0

Mole at equilibrium

    (1–x)                  x                 x

   (1–x)   (1–x)             2x

  (1–x)                                2x             x

Total moles at equilibrium (solid not included)




Mole fraction

                    \[\frac{x}{2x}=\frac{1}{2}\]             \[\frac{1}{2}\]

         \[\left( \frac{1-x}{1+x} \right)\]    \[\left( \frac{2x}{1+x} \right)\]

                                         \[\frac{2}{3}\]            \[\frac{1}{3}\]

Partial pressure

                          \[\frac{P}{2}\]               \[\frac{P}{2}\]

      \[P\left( \frac{1-x}{1+x} \right)\]  \[P\left( \frac{2x}{1+x} \right)\]

                                         \[\frac{2P}{3}\]         \[\frac{P}{3}\]






Relationship between equilibrium constant and DG°

DG for a reaction under any condition is related with DG° by the relation, \[\Delta G=\Delta G{}^\circ +2.303\ RT\log Q\]

 Standard free energy change of a reaction and its equilibrium constant are related to each other at temperature T by the relation, \[\Delta {{G}^{o}}=-2.303\,RT\,\log K\]

For a general reaction \[aA+bB\] ? \[cC+dD\]

\[K=\frac{{{({{a}_{C}})}^{c}}\ {{({{a}_{D}})}^{d}}}{{{({{a}_{A}})}^{a}}\ {{({{a}_{B}})}^{b}}}\]

Where a represent the activity of the reactants and products. It is unit less.

 For pure solids and liquids: \[a=1\].

For gases: \[a=\] pressure of gas in atm.

For components in solution: \[a=\] molar concentration.



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