Quote of the day Only entropy comes easy

Quote of the day: Only entropy comes easy. Anton Chekhov Announcements • If you don’t have a clicker with you, sign in after class • Chapter 19 Homework has been assigned in OWL • Exam #1: • One week from today • Covers Chapter 5, 8. 4, and 19 (up to page 9 -14) • Study guide posted next week

Spontaneity= Will a reaction happen under these conditions? A ball rolls downhill Na metal + H 2 O => Na. OH + H 2 Ice melts at 25°C (ΔH= +6. 01 k. J/mol) Water freezes at -10°C (ΔH= -6. 01 k. J/mol) Does ΔH favor spontaneity?

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

Trends in entropy Physical State Size Temperature Gas

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

Trends in Entropy

Trends in Entropy

Trends in entropy Physical State Size Temperature Gas

Which of the following has the greatest entropy? 1. 2. 3. 4. Cl 2(g) Cl(g) 2 Cl(g) H 2 O(s)

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

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

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

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?

Calculating S All other reactions N 2(g) + 3 H 2(g) 2 NH 3(g)