2. EQUILIBRIUM IN CHEMICAL PROCESSES – DYNAMIC EQUILIBRIUM

EQUILIBRIUM IN CHEMICAL PROCESSES

Like equilibria in physical systems it can also be achieved in chemical process involving reversible chemical reactions carried in closed container.  A + B ↔ C + D

The dynamic nature of chemical equilibrium can be demonstrated in the synthesis of ammonia by Haber’s process. Haber started his experiment with the known amounts of N₂ and H₂ at high temperature and pressure. At regular intervals of time he determined the amount of ammonia present. He also found out concentration of unreacted N₂ and H₂.
After a certain time he found that the composition of mixture remains the same even though some of the reactants are still present. This constancy indicates the attainment of equilibrium. In general, for a o can be shown by

According to the equilibrium law,

Where Kc is called equilibrium constant.

For a general reaction,

aA + bB ↔ cC + dD

For the reactio  H₂ + I₂ ↔ 2HI ;

For the reaction N₂ + 3H₂ ↔ 2NH₃

After a certain time the two reactions occur at the same rate and the system reaches a state of equilibrium. This can be shown by the given figure.

Equilibrium constant for the reverse reaction is the inverse of that for the forward reaction.

If the equilibrium constant for the reaction H₂ + I₂ ↔ 2HI is Kc, then that for the reverse reaction  2HI ↔ H₂ + I₂ is 1/Kc