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Ch.18 - Free Energy and Thermodynamics
All textbooksTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblem 55
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Chapter 18, Problem 55

Use data from Appendix IIB to calculate ΔSrxn ° for each of the reactions. In each case, try to rationalize the sign of ΔSrxn ° . a. C2H4(g) + H2(g) → C2H6(g)

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1
Identify the substances involved in the reaction: C2H4(g), H2(g), and C2H6(g).
Use Appendix IIB to find the standard molar entropy (S°) values for each substance: S°(C2H4), S°(H2), and S°(C2H6).
Apply the formula for the standard entropy change of the reaction: ΔS°_rxn = ΣS°(products) - ΣS°(reactants).
Substitute the S° values into the formula: ΔS°_rxn = [S°(C2H6)] - [S°(C2H4) + S°(H2)].
Rationalize the sign of ΔS°_rxn by considering the change in the number of gas molecules: The reaction goes from 2 moles of gas (C2H4 and H2) to 1 mole of gas (C2H6), which typically results in a decrease in entropy (ΔS°_rxn < 0).
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