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Lecture 18.4- Free Energy

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Section 18.4 Lecture for Honors Chem

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Lecture 18.4- Free Energy

  1. 1. Bellwork- Common ion A 1x10-3 M solution of PbCl2 does not precipitate solid lead chloride because the (concentration)2 is less than the Ksp, which is 1.6x10-5. Which of the following salts would cause precipitation of lead chloride if added to the solution described above? Explain WHY. KNO3 Pb(NO3)2 NaCl NaBr
  2. 2. 18.4 A spontaneous reaction occurs naturally and favors the formation of products at the specified conditions.
  3. 3. 18.4 A nonspontaneous reaction is a reaction that does not favor the formation of products at the specified conditions. Photosynthesis is a nonspontaneous reaction that requires an input of energy.
  4. 4. Spontaneous reactions produce substantial amounts of products at equilibrium and release free energy. Free energy is energy that is available to do work.
  5. 5. Entropy is a measure of the disorder of a system. •Physical and chemical systems attain the lowest possible energy. •The law of disorder states that the 2nd law of thermodynamics natural tendency is for systems to move in the direction of maximum disorder or randomness.
  6. 6. 18.4 Spontaneous processes often involve an increase in entropy.
  7. 7. For a given substance, the entropy of the gas is greater than the entropy of the liquid or the solid. Similarly, the entropy of the liquid is greater than that of the solid. Less entropy solid ⇒ liquid ⇒ gas more
  8. 8. 18.4 Entropy increases when a substance is divided into parts.
  9. 9. Entropy tends to increase in chemical reactions in which the total number of product molecules is greater than the total number of reactant molecules.
  10. 10. Entropy tends to increase when temperature increases. As the temperature increases, the molecules move faster and faster, which increases the disorder.
  11. 11. The Gibbs free-energy change is the maximum amount of energy that can be coupled to another process to do useful work. Change in Entropy Change in Temp in Enthalpy Kelvins ΔG is negative in spontaneous processes because the system loses free energy.
  12. 12. Gibbs Free-Energy
  13. 13. Gibbs Free-Energy
  14. 14. 1. Free energy from a reaction is the amount of energy that is a. absorbed by an entropy decrease. b. equal to the enthalpy change. c. wasted as heat. d. available to do work.
  15. 15. 18.4 Section Quiz. 2. Free energy is always available from reactions that are a. endothermic. b. nonspontaneous. c. at equilibrium. d. spontaneous.
  16. 16. 18.4 Section Quiz. 3. Choose the correct words for the spaces: Spontaneous reactions produce ________ and substantial amounts of _________ at equilibrium. a. free energy, products b. no free energy, reactants c. free energy, reactants d. no free energy, products
  17. 17. 18.4 Section Quiz. 4. Which of the following involves a decrease in entropy? a. Natural gas burns. b. A liquid freezes. c. Dry ice sublimes. d. Water evaporates.
  18. 18. 18.4 Section Quiz. 5. A reaction is spontaneous if a. enthalpy decreases and entropy increases. b. enthalpy increases and entropy increases. c. enthalpy decreases and entropy decreases. d. enthalpy increases and entropy decreases.
  19. 19. 18.4 Section Quiz. 6. Choose the correct words for the spaces: Gibbs free-energy change is the _________ amount of energy that can be ___________ another process to do useful work. a. maximum, coupled to b. maximum, duplicated by c. spontaneous, coupled to d. minimum, duplicated by