Negative entropy value for F- (aq) and OH-(aq)?

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SUMMARY

The discussion centers on the negative standard entropy values (S°) for the ions F- (aq) and OH- (aq). It is established that these negative values indicate a decrease in entropy when transitioning from gaseous F2 to aqueous F- ions. The participants explore the implications of negative entropy for single ions, particularly focusing on the unique properties of F- and OH- that contribute to their low entropy values, such as their electronegativity and the nature of their formation reactions.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically entropy (S°) and Gibbs free energy (ΔG°).
  • Familiarity with standard formation enthalpies (ΔH°) and their relation to entropy.
  • Knowledge of chemical reactions, particularly irreversible reactions and their impact on entropy.
  • Basic concepts of ionic species and their properties in aqueous solutions.
NEXT STEPS
  • Research the thermodynamic properties of other ions with negative entropy values.
  • Study the implications of electronegativity on the entropy of ions.
  • Learn about the relationship between reaction mechanisms and entropy changes.
  • Examine the standard enthalpy and entropy tables for various substances to identify patterns.
USEFUL FOR

Chemistry students, thermodynamics researchers, and professionals in chemical engineering who are interested in the thermodynamic behavior of ions and their implications in various reactions.

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I'm currently studying thermodynamics, and while looking through the chart of [tex]\Delta[/tex] H[tex]\circ[/tex], S[tex]\circ[/tex], and [tex]\Delta[/tex] G[tex]\circ[/tex] values for 200+ substances. Out of these, I noticed that two (F- (aq) and OH- (aq) have a negative S[tex]\circ[/tex] value. How can a single ion have a negative entropy? I understand that irreversible rxns and rxns with more moles of product than reactants have a negative S[tex]\circ[/tex] value, but I am having trouble seeing a negative entropy value for an ion. And why just F- and OH-? What makes them special? Electronegative? (For F- at least..)?

Thanks.
 
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Your table most likely lists values for the standard formation enthalpies and entropies. A negative So value just means that going from F2(g) to F-(aq) involves a decrease of entropy.
 

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