Chemical equilibrium is the state which occurs when the concentration of reactants and products participating in a chemical reaction exhibit no net change over time. The chemical equilibrium results when the rate of forward reaction and the rate of backward reaction are same in a reversible chemical reaction. Chemical equilibrium may also be called a "steady state reaction". At equilibrium chemical reactions have not stopped occurring, but the rates of formation of products and reactants from products has reached a balanced condition(constant), but not zero.
Reaction between H2 and I2 in a closed vessel.
When hydrogen and iodine reacted in a closed vessel at 717 K, hydrogen molecules combine with iodine
molecules to form hydrogen iodide molecules.
The HI molecules formed also begin to dissociate to form H2 and I2.
The concentrations of I2 and H2 decreases as the reaction progresses and the rate of
forward reaction decreases,at the same time the concentration of hydrogen iodide increases and therefore rate of backward
reaction increases. A stage is reached when the rate of backward reaction becomes equal to the rate of forward reaction, when
such a state is reached the system is said to be in equilibrium.
Types of equilibrium
Homogeneous Equilibrium:
An equilibrium condition in which all the products and reactants are in the same state of matter then the system is said to be in
Homogeneous Equilibrium.
Heterogeneous Equilibrium:
An equilibrium condition that involves more than one state of matter is called as Heterogeneous Equilibrium.