1. Figure: 19-01
Title:
Spontaneous expansion of an ideal gas into an evacuated space.
Caption:
In (a) flask B holds an ideal gas at 1 atm pressure and flask A is evacuated. In (b) the stopcock connecting the flasks has been opened. The ideal gas expands to occupy both flasks A and B at a pressure of 0.5 atm. The reverse process—all the gas molecules moving back into flask B—is not spontaneous.

2. Figure: 19-02
Title:
A spontaneous process.
Caption:
Elemental iron in the shiny nail in the top photograph spontaneously combines with H2O and O2 in the surrounding air to form a layer of rust—Fe2O3—on the nail surface.

3. Figure: 19-03
Title:
Spontaneity can depend on the temperature.
Caption:
At T > 0ºC ice melts spontaneously to liquid water. At T < 0ºC the reverse process, water freezing to ice, is spontaneous. At T = 0ºC the two states are in equilibrium and neither conversion occurs spontaneously.

4. Figure: 19-04a, b
Title:
Reversible flow of heat.
Caption:
Heat can flow reversibly between a system and its surroundings if the two have only an infinitesimally small difference in temperature, T. (a) Increasing the temperature of the system by T causes heat to flow from the system to the surroundings. (b) Decreasing the temperature of the system by T causes heat to flow from the surroundings into the system.

5. Figure: 19-05a-c
Title:
An irreversible process.
Caption:
Restoring the system to its original state after an irreversible process changes the surroundings. In (a) the gas is confined to the right half of the cylinder by a partition. When the partition is removed (b), the gas spontaneously (irreversibly) expands to fill the whole cylinder. No work is done by the system during this expansion. In (c), we can use the piston to compress the gas back to its original state. Doing so requires that the surroundings do work on the system, which changes the surroundings forever.

6. Figure: 19-06
Title:
Vibrational and rotational motions in a water molecule.
Caption:
Vibrational motions in the molecule involve periodic displacements of the atoms with respect to one another. Rotational motions involve the spinning of a molecule about an axis.

7. Figure: 19-08
Title:
Probability and the locations of gas molecules.
Caption:
The two molecules are colored red and blue to keep track of them. (a) Before the stopcock is opened, both molecules are in the right-hand flask. (b) After the stopcock is opened, there are four possible arrangements of the two molecules. Only one of the four arrangements corresponds to both molecules being in the right-hand flask. The greater number of possible arrangements corresponds to the greater disorder of the system. In general, the probability that the molecules will stay in the original flask is (1/2)n, where n is the number of molecules.

8. Figure: 19-09
Title:
Structure of ice.
Caption:
The intermolecular attractions in the three-dimensional lattice restrict the molecules to vibrational motion only.

9. Figure: 19-10
Title:
Dissolving an ionic solid in water.
Caption:
The ions become more spread out and random in their motions, but the water molecules that hydrate the ions become less random.

10. Figure: 19-11a, b
Title:
Entropy change for a reaction.
Caption:
A decrease in the number of gaseous molecules leads to a decrease in the entropy of the system. When the NO(g) and O2(g) in (a) react to form the NO2(g) in (b), the number of gaseous molecules decreases. The atoms have fewer degrees of freedom because of the formation of the new N—O bonds, and the entropy decreases.

11. Figure: 19-12a
Title:
Entropy and life.
Caption:
This ginkgo leaf represents a highly organized living system.

12. Figure: 19-12b
Title:
Entropy and life.
Caption:
Cyanobacteria absorb light energy and utilize it to synthesize the substances needed for growth.

13. Figure: 19-13
Title:
A perfectly ordered crystalline solid at and above 0 K.
Caption:
At absolute zero (left), all lattice units are in their lattice sites, devoid of thermal motion. As the temperature rises above 0 K (right), the atoms or molecules gain energy and their vibrational motion increases.

14. Figure: 19-14
Title:
Entropy as a function of temperature.
Caption:
Entropy increases as the temperature of a crystalline solid is increased from absolute zero. The vertical jumps in entropy correspond to phase changes.

15. Figure: 19-15
Title:
Molar entropies.
Caption:
In general, the more complex a molecule (that is, the greater the number of atoms present), the greater the molar entropy of the substance, as illustrated here by the molar entropies of three simple hydrocarbons.

16. Figure: 19-17a, b
Title:
Potential energy and free energy.
Caption:
An analogy between the gravitational potential-energy change of a boulder rolling down a hill (a) and the free-energy change in a spontaneous reaction (b). The equilibrium position in (a) is given by the minimum gravitational potential energy available to the system. The equilibrium position in (b) is given by the minimum free energy available to the system.

17. Figure: 19-18
Title:
Free energy and equilibrium.
Caption:
In the reaction of N2(g) plus 3 H2(g) in equilibrium with 2 NH3(g), if the reaction has too much N2 and H2 relative to NH3 (left), the equilibrium lies too far to the left (Q < K) and NH3 forms spontaneously. If there is too much NH3 in the mixture, the equilibrium lies too far to the right (Q > K) and the NH3 decomposes spontaneously into N2 and H2. Both of these spontaneous processes are "downhill" in free energy. At equilibrium (center), Q = K and the free energy is at a minimum (G = 0).

18. Figure: 19-19
Title:
Free energy and cell metabolism.
Caption:
This schematic representation shows part of the free-energy changes that occur in cell metabolism. The oxidation of glucose to CO2 and H2O produces free energy that is then used to convert ADP into the more energetic ATP. The ATP is then used, as needed, as an energy source to convert simple molecules into more complex cell constituents. When it releases its stored free energy, ATP is converted back into ADP.

19. Figure: UNE1
Title:
Exercise 19.1
Caption:
Two bulbs containing gas.

20. Figure: UNE2
Title:
Exercise 19.2
Caption:
Conversion of a solid to a gas.

21. Figure: UNE3
Title:
Exercise 19.3
Caption:
Chemical reaction.

22. Figure: UNE4
Title:
Exercise 19.4
Caption:
Graph of change in H and TS with temperature.

23. Figure: UNE5
Title:
Exercise 19.5
Caption:
Boxes representing a chemical reaction.

24. Figure: UNE6
Title:
Exercise 19.6
Caption:
Graph of free energy versus progress of reaction.

25. Figure: UNE35
Title:
Exercise 19.35
Caption:
Graph of entropy as a function of temperature.

26. Figure: UNE42
Title:
Exercise 19.42
Caption:
Structures of cyclopropane and propylene.

27. Figure: UNE106
Title:
Exercise
Caption:
Rubber band.

28. Figure: 19-T01
Title:
Table 19.1
Caption:
A Comparison of the Number of Combinations That Can Lead to a Royal Flush and to a "Nothing" Hand in Poker.

29. Figure: 19-T02
Title:
Table 19.2
Caption:
Standard Molar Entropies of Selected Substances at 298 K.

30. Figure: 19-T03
Title:
Table 19.3
Caption:
Conventions Used in Establishing Standard Free Energies.

31. Figure: 19-T04
Title:
Table 19.4
Caption:
The Effect of Temperature on the Spontaneity of Reactions.

32. Figure:
Title:
Table 19.5
Caption:
Relationship Between Gº and K at 298 K.