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Catalyst

Learn about enthalpy, entropy, and Gibbs free energy to predict spontaneous reactions in chemistry. Find out how to calculate spontaneity and the factors affecting it. Engage in activities to deepen your understanding.

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Catalyst

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  1. Catalyst Come in quietly and begin working on the Quiz that is on your desk End

  2. Learning Log Assessment • Rate yourself 1 – 4 on LTs 7.1-7.7

  3. Checklist Manifesto! • How do I know which equation to use? • Does it have specific heat or enthalpy?? • Then use calorimetry! • Does it give you ΔH or ΔT • If ΔH then use q = mΔH • If ΔT then use q = m x Cp x ΔT • Box the one it’s asking you to find! • Plug in the right numbers and solve!

  4. Connect 4

  5. Lecture 7.5 – Gibbs Free Energy

  6. Today’s Learning Targets • 7.8 – I can discuss what entropy is, the conditions under which it is favored, and how entropy changes when we change the phase of a solution. • 7.9 – I can describe what enthalpy is, how it relates to the idea of endothermic and exothermic, and how it changes the favorability of a reaction. • 7.10 – I can use the idea of Gibbs Free Energy to predict whether a reaction will be spontaneous.

  7. Today’s Focus Question • What chemistry allows for the breakdown of Flamin’ Hot Cheetos to occur?

  8. What are enthalpy and entropy?

  9. Exothermic Endothermic

  10. I. Entropy and Enthalpy • Enthalpy is a measure of energy a system has. • Endothermic= +ΔH • Exothermic= -ΔH • Entropy is the measurement of the disorder of a system. • Lots of Disorder = +ΔS • Minimal Disorder = -ΔS

  11. How do we predict spontaneous reactions?

  12. I. Favorability of Reactions • Only certain values of ΔH and ΔS are favorable • Reactions favor disorder, so +ΔS is favored. • Reactions favor reactions that release energy, so –ΔH is favored.

  13. Class Example • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. You run the following reaction: N2 (g) + O2(g)  2 NO (g) You have ΔH = 180.7 kJ and ΔS = 24.7 J/K

  14. Table Talk • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. • You run the following reaction: • P4 (g) + 6 Cl2 (g)  4 PCl3 (g) • You have ΔH = -190.2 kJ and ΔS = 423.4 J/K

  15. Stop and Jot • Without calculating, predict if the following reaction will be spontaneous. If it is spontaneous, specify under what conditions. • You run the following reaction: • N2 (g) + 3 H2 (g)  2 NH3 (g) + 567 kJ

  16. White Board Races

  17. White Board Questions • Using only the signs of Ho and So, predict the signs and temperature dependence. • CH3OH (l) + 3/2 O2 (g)  CO2 (g) + 2 H2O (g) • Exothermic reaction • 2. The vaporization of water • 3. CO (g) + H2O (g)  CO2 (g) + H2 (g) • Ho = -41.2 kJ and So = -135 J/K • 4. The condensation of water • 5. P4 (g) + 6 Cl2 (g)  4 PCl3 (g) • The reaction is endothermic • 6. N2 (g) + O2(g)  2 NO (g) • The reaction is endothermic • 7. The freezing of carbon dioxide

  18. How do we calculate spontaneity?

  19. I. Gibbs Free Energy (ΔG) • We can calculate ΔG by: ΔG = ΔH – TΔS • ΔG is the Gibbs Free Energy • T is Temperature (in KELVIN) • A positive ΔG means the reaction is NOT spontaneous. • A negative ΔG means that the reaction IS spontaneous

  20. Class Example • For the vaporization reaction: Br2 (l)  Br2 (g) ΔH = 31 kJ/mol and ΔS = 93 kJ/(mol x K). Is this spontaneous at 298 K?

  21. Table Talk • A reaction has ΔH = -385 kJ and ΔS = -36 kJ/(mol x K). Calculate ΔG at 25 oC and state whether the reaction is spontaneous.

  22. Stop and Jot • You have a reaction with a ΔH = 125 kJ/mol, ΔS = 0.0350 kJ/(mol x K), and T=293 K. Is this spontaneous and how could you make this reaction spontaneous?

  23. BINGO!

  24. BINGO Questions • I have a reaction with a positive enthalpy and a negative entropy. Is this a spontaneous or non-spontaneous reaction? • I have a reaction with a negative enthalpy and a positive entropy. Is this a spontaneous or non-spontaneous reaction? • I turn solid ice into liquid water. Does this increase or decrease the entropy of the system? • Determine the ΔG of the hydrolysis of urea when it is 25 oC, ΔH=119.2 kJ/mol, and ΔS=0.3548 kJ/(mol x K).

  25. BINGO Questions • Calculate ΔG for the following reaction: ΔH = -85.2 kJ, T= 127 oC, and ΔS = 0.125 kJ/(mol x K). • Calculate ΔG for the following reaction: ΔH = -275 kJ, T= 773 oC, and ΔS = 0.450 kJ/(mol x K). • A reaction has ΔH = 98 kJ/mol and ΔS = 292 J/(mol x K). If the temperature is 25 oC, what is the ΔG? • For the vaporization reaction Br2 (l)  Br2 (g) ΔH = 31 kJ/mol and ΔS = 93 kJ/(mol x K). At what temperature will it become spontaneous?

  26. BINGO Questions • Which is more favorable: more disorder or less disorder? • Which is more favorable: an exothermic reaction or an endothermic reaction?

  27. Learning Log Assessment • Rate yourself 1 – 4 on LTs 7.8, 7.9, and 7.10.

  28. Online Simulator • Use the online simulator to explore the relationship between entropy, enthalpy and the favorability of a reaction. • You may work with a partner

  29. Work Time • Begin working on your “Homework 7.5” • There will be an exit slip after this activity

  30. Exit Slip 1. You have a reaction that has a +ΔS and a +ΔH. Under what conditions would this reaction be spontaneous? 2. For the reaction: NH4Cl (s)  NH3 (g) + HCl (g) ΔH = 176 kJ/mol and ΔS=0.285 kJ/(mol x K) and T = 400 K. Determine ΔG and state whether this is a spontaneous reaction.

  31. Learning Log Assessment • Using your exit slip score, re-rate yourself on LTs 7.8, 7.9, and 7.10

  32. Review Stations • Station 1 – LT 7.1 • Station 2 – LT 7.2 • Station 3 – LT 7.3 • Station 4 – LT 7.4 • Station 5 – LT 7.5 • Station 6 – LT 7.6 • Station 7 – LT 7.7 • Rotate between the 7 stations (10 for honors) • Honors Station 8,9,10 – LT 7.8, 7.9, 7.10 ROTATE!

  33. Closing Time • Homework 7.5 – Gibbs Free Energy • Test Tuesday!

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