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Chapter 17B Reaction Energy Entropy & Free Energy

Chapter 17B Reaction Energy Entropy & Free Energy. West Valley High School General Chemistry Mr. Mata. Standard 8a. Students will know how enthalpy, entropy, and free energy are related. Essential Questions. What factors influence the enthalpy, entropy, and free energy?.

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Chapter 17B Reaction Energy Entropy & Free Energy

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  1. Chapter 17BReaction EnergyEntropy & Free Energy West Valley High School General Chemistry Mr. Mata

  2. Standard 8a Students will know how enthalpy, entropy, and free energy are related.

  3. Essential Questions What factors influence the enthalpy, entropy, and free energy?

  4. Hess’ LawEnthalpy of Reaction ΔHrxn = Hproducts – Hreactants - ΔH = exothermic + ΔH = endothermic

  5. Entropy, ΔS • Entropy • measure of relative disorder. • Thermodynamics tells us the universe moves towards disorder (entropy). ΔS = Sproducts – Sreactants

  6. Entropy, ΔS Entropy helps predict whether a reaction will be spontaneous. Solids have very low entropy Gases have very high entropy Solutions also have high entropy

  7. Entropy Values Reaction entropy; 2KClO3(s) 2KCl(s) + 3O2(g) 2 solids  2 solids + 3 gases Entropy increases in this reaction.

  8. Entropy Values • A positive ΔS = increase in entropy • A negative ΔS = decrease in entropy Do not confuse entropy and enthalpy! • Moving towards spontaneity: • Negative Enthalpy (-ΔH) • Positive Entropy (+ΔS)

  9. Gibb’s Free Energy Measure of system energy change. Gibbs Free Energy, ΔG Named after American chemist, J. Willard Gibbs, who developed an equation to relate enthalpy & entropy.

  10. Free Energy, ΔG • Free energy, ΔG, allows us to assign a value to an entire reaction. • The basic equation is: ΔG = ΔH -TΔS

  11. Gibbs Free Energy, ΔG • A negative Gibbs Energy (-ΔG): Spontaneous, Product favored • A positive Gibbs Energy (+ΔG): Nonspontaneous, Reactant favored

  12. In conclusion… • Enthalpy, ΔH • - ΔH = exothermic (heat out) • + ΔH = endothermic (heat in) • Entropy, ΔS • - ΔS = decrease in entropy (stable) • + ΔS = increase in entropy (unstable) • Gibbs Free Energy, ΔG • - ΔG = spontaneous • + ΔG = nonspontaneous

  13. Chapter 17 SUTW Prompt Describe how we calculate enthalpy, entropy, and free energy for chemical reactions. Complete a 11 -12 sentence paragraph using the SUTW paragraph format. Hilight using green, yellow, and pink. Due Date: Monday, March 26, 2018 at beginning of your regular class period.

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