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Thermochemistry Part III

Thermochemistry Part III. Entropy and Gibbs Free Energy. 1. Entropy. Reactions generally move to a lower energy state. Entropy (S) : a measure of the disorder or randomness of the particles in a system spontaneous processes always proceed in the direction of more entropy (more disorder)

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Thermochemistry Part III

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  1. Thermochemistry Part III Entropy and Gibbs Free Energy

  2. 1. Entropy • Reactions generally move to a lower energy state. • Entropy (S) : a measure of the disorder or randomness of the particles in a system • spontaneous processes always proceed in the direction of more entropy (more disorder) • DS = Sproducts– Sreactants • DS is positive when there is more disorder in the products than the reactants

  3. 2. Predicting Entropy • Entropy Increases when: • Going from solid to liquid to gas • Fewer moles  more moles example: 2 SO3 (g)  3SO2 (g) + O2 (g) - simpler molecules  more complex - separate solute + solvent  solution • Increasing temperature always increases entropy (S)

  4. 3. Free Energy • Gibbs Free Energy (G): reflects the balance between the two driving forces of a reaction, entropy and enthalpy • Depends on enthalpy (H) and entropy (S) • DG = DH – TDS • Free energy tells us if the reaction is product favored, also referred to as spontaneous or not. • + DG = nonspontaneous • - DG = spontaneous

  5. Product or Reactant favored reactions depend on DH, DS, and Temperature

  6. 4. Summary of Variables • Enthalpy (H): heat of rxn + DH = endothermic - DH = exothermic (favorable) • Entropy (S): disorder of reaction + DS = more disorder (favorable) - DS = less disorder • Gibbs Free Energy (G): spontaneity of rxn + DG = nonspontaneous - DG = spontaneous

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