Equilibrium

There are 2 conditions for equilbrium to be established for a certain reaction:
1. Forward and backward reaction occur at the same rate.
2. The concentration of reactants and products remain constant.
Equilibrium can only happen in a closed system, where the reactants and/or products do not come in contact with the surroundings.
Equilibrium is dynamic, meaning that at a microscopic level, the reaction does not stop as the reactants are continuously changed to products and the products are continuously changed to the reactants. However, at a macroscopic level, there is no change in the properties such as pressure, colour, pH, or concentration.

Physical equilibrium does not involve a chemical reaction, rather a change in the state, for example from liquid to gas and gas to liquid.
Even for this type of equilibrium, similar conditions apply:
1. The rate of forward process is equal to the rate of backward process.
2. The volume of liquid remains constant.
Equilibrium can only occur in a closed system.
Similiar to chemical equilibrium, the equilibrium is dynamic at a microscopic level where the liquid is getting continuously evaporated and the gas is getting continuously condensed, but at a macroscopic level the properties remain the same, such as color.