ü Rate of forward reaction = Rate of backward reaction
ü Concentration of all entities become constant
ü Dynamic equilibrium
ü Can be attained in closed container only
ü Catalyst does not change state of equilibrium but helps in attaining it quickly
ü Gibb’s free energy is minimum and entropy of universe maximum
ü Can be achieved from either side
ü Approach toward equilibrium is spontaneous
Extent of a reaction at equilibrium varies with the experimental condition such as concentration of entities, temperature etc.
Normal melting point: at atm pressure, the temperature at which both liquid and solid phases are at equilibrium.
LAW OF CHEMICAL EQUILIBRIUM
For a general reaction aA + bB cC + dD
This equation is also known as the law of mass action because in earlier days, concentration = active mass.
K depends only on temperature. It is independent of concentration of entities, catalyst, addition of inert gas etc.
Consider a reaction A B k1
And B A k2
Then k1 = 1/k2
And if A B k1 ;
C D k2
And A + B C + D k
Then K = k1k2
Effect of temperature on K
K = Ae-Ea/RT
A and Ea are assumed to be temperature independent.
If K1 and K2 are eq. constants at temperatures T1 and T2 respectively then
For endothermic reaction, T is proportional to K
For exothermic reaction, T is inversely proportional to K
Le – Chetelier’s Principle
" If a system at equilibrium is subjected to a change in its pressure, temperature, concentration etc., the system adjusts itself in such a way to nulify the effect of that change." But the effect may not be nulified completely.
Effect of concentration
concept of reaction quotient(Q)
This ration is calculated at given conditions. If Q>K, reaction shifts in backward direction
If Q=K, reaction is at equilibrium and if Q<K, reaction goes in forward direction.
Effect of Pressure
An increase in Pressure (due to decrease in Volume) favours the reaction in the direction that produces smaller no. of moles of gaseous substance.
Effect of temperature explained before.
Addition of inert gas at constant pressure