What are equilibrium processes? Explain equilibrium in Physical and Chemical processes with examples.

Explanation

Equilibrium State (or) Equilibrium Process : The state at which the velocity of forward reaction becomes equal to the velocity of backward reaction or reverse seaction is called .equilibrium state.. Consider a reversible reaction.
`A+B hArr C+D` taking place in a closed vessel. At the beginning we have only the reactants A and B. Their concentrations are maximum. As the reaction proceeds the reactants A and B change into the products C and D. The Equilibrium concentrations of the products increase gradually.
The rate of forward reaction diminishes while the reverse reaction sets in and proceeds with increasing speed. A state is soon reached where the speeds of forward and backward. reactions become equal. If the rate of forward reaction `V_(f)` = The rate of reverse reaction `(V_(b))`.
The system is said to have attained a state of equilibrium. Once equilibrium is reached there is no further change in the composition of the system. The system appears to be stand still although it is. dynamic. The products are formed by forward reaction just as fast as they change back into reactants by the reverse reaction.
The state at which the rate of forward reaction is equal to the rate of the reverse reaction in a reversible reaction is known as the equilibrium state or chemical equilibrium.
Examples:
(i) Equilibrium physical processes :
(a) Equilibrium between two phases (i.e.), physical transformation processes.
solid `hArr` Liquid (melting or fusion)
(b) Equilibrium between two different allotropic forms of same substance
`alpha`- Sulphur ` hArr beta-` Sulphur
(ii) Equilibrium chemical processes :
`(a) N_(2)(g)+3H_(2)(g) hArr 2NH_(3)(g)`
(b) `2SO_(2)(g)+O_(2)(g) hArr 2SO_(3) (g)`
(c) `H_(2)(g)+I_(2)(g) hArr 2HI(g)`