Chapter 17B Reaction Energy Entropy & Free Energy

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Presentation transcript:

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?

Hess’ Law Enthalpy of Reaction ΔHrxn = Hproducts – Hreactants - ΔH = exothermic + ΔH = endothermic

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

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

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

Negative Enthalpy (-ΔH) Positive Entropy (+ΔS) 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)

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.

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

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

In conclusion… Enthalpy, ΔH Entropy, ΔS Gibbs Free Energy, ΔG - 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

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.