Entropy and feasibility of reactions

Understanding Entropy

Gases have the highest entropy because their particles can move freely and randomly.
Solids have the lowest entropy as their particles are fixed in place.
Liquids have an intermediate entropy value as their particles have some freedom of movement.
The entropy of a system usually increases during a chemical reaction. This is due to the conversion of reactants into products, often forming gaseous products from solid or liquid reactants.

The total entropy change for a reaction (∆Stotal) can be calculated by adding the entropy change of the environment (∆Ssurroundings) and the entropy change of the system (∆Ssystem).
∆Ssystem can be calculated using the equation: ∆Ssystem = ΣSproducts - ΣSreactants
∆Ssurroundings can be calculated from the enthalpy change of the reaction (∆H) and the temperature in kelvin (T), using the equation: ∆Ssurroundings = -∆H / T

A reaction is feasible if the total entropy change for a reaction (∆Stotal) is positive, which implies the overall disorder of the universe increases due to the reaction.
If ∆G (Gibbs free energy) of a reaction is negative, the reaction is spontaneous and feasible under constant temperature and pressure. ∆G can be calculated from the equation: ∆G = ∆H - T∆Ssystem
However, a positive ∆Stotal does not guarantee a reaction will occur. Other factors such as kinetic barriers (e.g., activation energy) may prevent a feasible reaction from occurring.

For endothermic reactions, the heat absorbed from the surroundings increases the entropy of the system, contributing to a positive ∆Stotal.
Dissolving a solid in a solvent usually results in an increase in entropy due to increased disorder.
Chemical reactions that produce more moles of gas result in an increase in entropy.