Final answer:
To derive the entropy change formula (ΔS) for a polycondensation reaction of an ideal gas, use ΔS⁰ = ΣnS°(products) - ΣnS°(reactants), where 'n' is the stoichiometric coefficient. This applies when dealing with gaseous reactants and products and can also account for changes in pressure using the ideal gas relationship ΔS = nRln(P2/P1).
Step-by-step explanation:
To derive the formula for entropy change (ΔS) in a polycondensation reaction for an ideal gas, we can utilize the standard entropy values (Sº) of the reactants and products. The standard entropy change for the reaction is given by the equation ΔS⁰ = ΣnS°(products) - ΣnS°(reactants), where 'n' represents the stoichiometric coefficient from the balanced chemical equation. For example, the entropy change for the formation of liquid water from gaseous hydrogen and oxygen is calculated using the standard entropies of the respective molecules and applying this equation.
For a polycondensation reaction, if the products and reactants are in their gaseous state, the value of ΔS can also be affected by changes in pressure. According to the equation derived from the ideal gas law, P = cRT, where 'c' represents the concentration and 'P' the pressure, the entropy change associated with a change in pressure can be expressed using concentrations: ΔS = nRln(P2/P1). However, this applies under the assumption that the solute behaves like an ideal gas within the solution, which may not always hold true for reactions involving condensed phases (liquids and solids).