1. Announcements If you don’t have a clicker with you, sign in after class If you don’t have a clicker with you, sign in after class Chapter 19 Homework has been assigned in OWL Chapter 19 Homework has been assigned in OWL Exam #1: Exam #1: One week from today Covers Chapter 5, 8.4, and 19 (up to page 9-14) Study guide posted next week Quote of the day: Only entropy comes easy. Anton Chekhov Anton Chekhov

2. Spontaneity= Will a reaction happen under these conditions?  A ball rolls downhill  Na metal + H 2 O => NaOH + H 2  Ice melts at 25°C ( Δ H= +6.01 kJ/mol)  Water freezes at -10°C ( Δ H= -6.01 kJ/mol)  Does Δ H favor spontaneity?

3. Entropy A measure of randomness. Units of J/K.

4. Trends in entropy  Physical State  Size  Temperature  Gas

5. Trends in Entropy Larger and more complex molecules have greater entropies.

6. Trends in Entropy

8. Trends in entropy  Physical State  Size  Temperature  Gas

9. Which of the following has the greatest entropy? 1.Cl 2 (g) 2.Cl(g) 3.2Cl(g) 4.H 2 O(s)

10. Which of the following gas molecules has the greatest standard molar entropy at 25°C? 1.C 2 H 2 2.CH 2 CH 2 3.CH 3 CH 3 4.All would have the same entropy

11. Entropy is a State Function  Like total energy, E, and enthalpy, H, entropy is a state function.

12. Entropy and Physical StatesEntropy and Physical States  Entropy increases with the freedom of motion of molecules.  Therefore, S ( g ) > S ( l ) > S ( s )

13. Calculating  S Special Case: Phase Changes Heat of fusion (melting) of ice is 6000 J/mol. What is the entropy change for melting ice at 0 o C?

14. Calculating  S All other reactions N 2 (g) + 3 H 2 (g)  2 NH 3 (g)