1. THE 2ND LAW OF THERMODYNAMICS:
3. entropy
a useful property, defined by scientists, that describes a measure of randomness or disorder
molecular: S=k[ln(W)], where k is Boltzmann’s constant and W is the number of ways the molecules can be arranged.
a state function
THE 2ND LAW OF THERMODYNAMICS:
1. There is a property of the system called entropy.
2. In any spontaneous process the combined entropy of the system plus the surroundings must increase.
Recall the 1ST LAW OF THERMODYNAMICS
1. There is a property of the system called energy.
2. The energy of a closed system is conserved.
Chapter 17 Notes

2. THE 3RD LAW OF THERMODYNAMICS:
At 0 Kelvin, the entropy of a perfect crystalline substance in exactly 0.
1. Entropy values found in tables are absolute values (compared to enthalpy and free energy values which are relative***).
2. The 2nd and 3rd laws together lead to the following: the temperature of 0 Kelvin cannot be achieved.
gases have higher entropy than solids (pure substance)
mixtures usually have higher entropy than pure components
exception: HF(g) vs. HF(aq) WHY?
larger molecules have higher entropy than smaller
more complex molecules have higher entropy than simple
Chapter 17 Notes

3. 1. In which of the following does H2O have the highest entropy?
Some examples
1. In which of the following does H2O have the highest entropy?
a. Ba(OH)2•8H2O (s) b. H2O(g)
c. H2O(l) d. H2O(s)
2. Does the entropy of the system (increase / decrease / stay the same) for the reaction: PCl5(s)PCl3(l)+Cl2(g)?
Chapter 17 Notes

4. 3. Calculate Srxn° for the reaction
H2(g) + 1/2O2(g)H2O(l)
using data from Appendix B.1.
4. Calculate Hrxn° for the reaction
H2(g) + 1/2O2(g)H2O(l)
using data from Appendix B.1.