17.6 : Entropy Changes in Chemical Reactions and How to Calculate ΔS°RXN: Standard State: Pure gas at 1atmPure liquid or solid at 1atm and 25°CPure substance in solution at 1MΔS°RXN = S°products - S°reactantsΔS°RXN= the standard entropy change for a reactionHOW TO COMPARE RELATIVE ENTROPIES: Effect of State of Matter (for same substances): The solid form would have the lowest S° and the gas form would have the highest S°. The liquid would be in between, higher than the solid but lower than the gas. Effect of Molar Mass (for elements in the same state of matter): S° increases as molar mass increases for elements in the same state of matter. Effect of Molecular Complexity: S° increases with increasing molecular complexity for molecules in the same state of matter. *A molecule would have a higher S° than an atom. Effect of dissolution: Aqueous solutions have higher S° than solids because they completely dissociate into two ions in
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