Mention if entropy of the system increases or decreases in each of the following cases: (1) Boiling of water.
(2) `2O_(3)(g)to3O_(2)(g)`
(3) Sublimation of solid iodine
(4) `NH_(4)Cl(s)toNH_(3)(g)+HC l(g)`.

Explanation

The change in entropy in a phase transition or in a reacction depends on the following factors.
(i) For a given amount of substance, the entropy of the substance in different physical states varies in the order: `overline(S_(gas)) gt overline(S)_("liquid") gt overline(S)_("solid")`, where `overline(S)` is the molar entropy. because of this, the entropy of the system increases in the phase change such as liquid`to`vapour, solid`to`liquid and solid`to`vapour, while it decrease in the phose changes such as liquid`to`solid, vapour`to`liquid and vapour`to`solid.
(ii) (a) In a reaction, if the reactants are solids or liquids or in a dissolved state in solution and they converts into gaseous product, then the entropy of the system increases. (b) if the number of gaseous particles (atoms or molecules) in a reaction increases or decreases, then the entropy of the system increases or decreases.
(1) Increases (liquid`to`vapour transition).
(2) Increases (solid`to`gas transition).
(3) Increases (the number of gaseous particles increases).
(4) Increases (gaseous substances are formed from a solid reactant).