Final answer:
The change in entropy for a chemical reaction is determined using the 'products minus reactants' rule, involving subtraction of summed standard molar entropies of reactants from products, considering stoichiometric coefficients. This calculation can hint at the reaction's progression towards more disordered states or gas phase formation.
Step-by-step explanation:
To determine the change in entropy (ΔS°) for a chemical reaction, one must apply the 'products minus reactants’ rule. This involves subtracting the sum of the standard molar entropies (S°) of the reactants from the sum of the standard molar entropies of the products, taking into account the stoichiometric coefficients. Specifically, the formula is ΔS° = nSº (products) - mS° (reactants), where 'n' and 'm' are the stoichiometric coefficients of the respective products and reactants.
In practice, you would first write the balanced chemical equation for the reaction. Then, identify the absolute entropies of each species from a data source such as a table of standard molar entropies. Multiply the entropy of each compound by its coefficient in the reaction equation and sum the entropies for both sides of the equation. Finally, subtract the total entropy of the reactants from that of the products to find ΔS°. An increase in entropy is often associated with the transition from a more ordered to a more disordered state, an increase in the number of moles of gas, or the absorption of heat in a reversible process.