The entropy change for the reaction 2O3(g) → 3O2(g) can be calculated using the standard entropy values of the reactants and products. The standard entropy change for a reaction is given by the equation:

ΔS° = ΣnS°(products) - ΣmS°(reactants)

where ΔS° is the standard entropy change, n is the stoichiometric coefficient of each product, m is the stoichiometric coefficient of each reactant, and S° is the standard entropy of each species.

For the given reaction, the standard entropy change is:

ΔS° = [3S°(O2(g))] - [2S°(O3(g))]

Using the standard entropy values for O2(g) (205.1 J/mol·K) and O3(g) (238.9 J/mol·K), we can calculate the entropy change:

ΔS° = [3 × 205.1 J/mol·K] - [2 × 238.9 J/mol·K] = -67.5 J/mol·K

The negative value of ΔS° indicates that the entropy of the system decreases as the reaction proceeds. This means that the reaction leads to a more ordered arrangement of molecules, with fewer possible microstates.