Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.
is positive when randomness increases and is negative when randomness decreases.
When the solid changes to liquid to gas ,the randomness of particles increases and hence is positive and thus the entropy increases.
Entropy is a measure that is used to calculate the amount of energy in the particles, this is related to the temperature of the particles and how they are capable of perform work, if the randomness in the particles of the element increases the entropy increases and the more movement there is in the substance the higher the temperature and the randomness as you know changing from solid to liquid, or to gas, the temperature needs to increase as well as the randomness.
