The important characteristics of equilibrium state are,
(1) Equilibrium state can be recognised by the constancy of certain measurable properties such as pressure, density, colour, concentration etc. by changing these conditions of the system, we can control the extent to which a reaction proceeds.
(2) Equilibrium state can only be achieved in close vessel.
(3) Equilibrium state is reversible in nature.
(4) Equilibrium state is also dynamic in nature.
(5) At equilibrium state, Rate of forward reaction = Rate of backward reaction (6) At equilibrium state, DG = 0, so that DH = TDS.
| \[\Delta n=0\,;\,\,{{K}_{p}}={{K}_{c}}\] | \[\Delta n<0\] ; \[{{K}_{p}}<{{K}_{c}}\] | more...
Factors which Change the State of Equilibrium: Le-Chatelier's Principle.
Le-Chatelier and Braun (1884), French chemists, made certain generalizations to explain the effect of changes in concentration, temperature or pressure on the state of system in equilibrium. When a system is subjected to a change in one of these factors, the equilibrium gets disturbed and the system readjusts itself until it returns to equilibrium. The generalization is known as Le-Chatelier's principle. It may stated as:
“Change in any of the factors that determine the equilibrium conditions of a system will shift the equilibrium in such a manner to reduce or to counteract the effect of the change.”
The principle is very helpful in predicting qualitatively the effect of change in concentration, pressure or temperature on a system in equilibrium. This is applicable to all physical and chemical equilibria.
(1) Effect of change of concentration : According to Le-Chatelier's principle, more...
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)
In the following reversible chemical equation.
\[A\] \[\rightleftharpoons \] \[yB\]
Initial mole 1 0
At equilibrium (1–x) yx x = degree of dissociation
Number of moles of \[A\] and \[B\] at equilibrium \[=1-x+yx=1+x(y-1)\]
If initial volume of 1 mole of A is V, then volume of equilibrium mixture of \[A\] and \[B\] is,\[=[1+x(y-1)]V\]
Molar density before dissociation,
\[D=\frac{\text{molecular}\ \text{weight}}{\text{volume}}=\frac{m}{V}\]
Molar density after dissociation, \[d=\frac{m}{[1+x(y-1)]V}\];\[\frac{D}{d}=[1+x(y-1)]\] ; \[x=\frac{D-d}{d(y-1)}\]
\[y\] is the number of moles of products from one mole of reactant. \[\frac{D}{d}\] is also called Van’t Hoff factor.
In terms of molecular mass,\[x=\frac{M-m}{(y-1)\,m}\]
Where \[M=\] Initial molecular mass,
\[m=\] molecular mass at equilibrium
Thus for the equilibria
(I) \[PC{{l}_{5(g)}}\] \[\rightleftharpoons \] \[PC{{l}_{3(g)}}+C{{l}_{2(g)}},y=2\]
(II) \[{{N}_{2}}{{O}_{4(g)}}\] \[\rightleftharpoons \] \[2N{{O}_{2(g)}},\ y=2\]
(III) \[2N{{O}_{2}}\] ? \[{{N}_{2}}{{O}_{4}},\ y=\frac{1}{2}\]
\[\therefore \] \[x=\frac{D-d}{d}\] (for I and II) and \[x=\frac{2(d-D)}{d}\] (for III)
Also \[D\times 2=\] Molecular weight (theoretical value)
\[d\times 2=\] Molecular weight (abnormal value) more...
Substances, which allow electric current to pass through them, are known as conductors or electrical conductors. Conductors can be divided into two types,
(1) Conductors which conduct electricity without undergoing any chemical change are known as metallic or electronic conductors.
(2) Conductors which undergo decomposition (a chemical change) when an electric current is passed through them are known as electrolytic conductors or electrolytes.
Electrolytes are further divided into two types on the basis of their strengths,
(i) Substances which almost completely ionize into ions in their aqueous solution are called strong electrolytes. Degree of ionization for this type of electrolyte is one i.e., \[\alpha \approx 1\].
For example : \[HCl,\ {{H}_{2}}S{{O}_{4}},\ NaCl,\ HN{{O}_{3}},\ KOH,\ \]\[NaOH,\ \] \[HN{{O}_{3}},AgN{{O}_{3}},\ CuS{{O}_{4}}\] etc. means all strong acids, bases and all types of salts.
(ii) Substances which ionize to a small extent in their aqueous solution are known as weak electrolytes. Degree of ionization for more...
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