1. CHEM 433 - 10/21/11 IV. 2nd Law of THERMO
• T dep. (heating/cooling) -> Measuring Sm°
• Third Law Entropies
- Standard Reaction Entropy Changes
- T dependence of S
READ: CHAPTER 3…
HW #5 : Out when I get that far ….

2. How to Measure molar S:
Measure Cp at many T’s
Fit to equaiton and integrate: Cp/T dT)
Measure trsS (as needed)
Add up all the parts - this is eqn on board…

3. (s) vs. (l) vs. (g) ?
Size ? (Svib)
Why are most gas
values lower than CO2?
(this is subtle…)

4. Nernst Heat Theorem:
For all processes: S —> 0 as T—> 0 (provided all substances are perfectly crystalline…)
3rd LAW of THERMO:
The entropy of a perfect crystalline substance is zero at T=0.
3rd Law Entropies:
Molar entropies obtained via assumption that S(0) = 0 (for all substances - crystalline or otherwise…)

5. For: H2 (g) + 1/2 O2 (g) —> H2O (l) rS° = ?
Sm° =
(all values in J/K mol at 298K…)
BTW: we calculated Ssurr for this last week -
—> ~1000 J/K mol (or 1 kJ/K mol)