1. Equilibrium

2. Copyright © Houghton Mifflin Company.All rights reserved. 16–2 Equilibrium can be analogous to traffic flowing both ways on a bridge, such as San Francisco's Golden Gate Bridge. Source: James Martin/Stone/Getty Images

3. Copyright © Houghton Mifflin Company.All rights reserved. 16–3 Refrigeration prevents food spoilage.

4. Copyright © Houghton Mifflin Company.All rights reserved. 16–4 Figure 16.1: (a) A sample containing a large quantity of reddish-brown NO 2 gas. (b) As the reaction to form colorless N 2 O 4 occurs, the sample becomes lighter brown. (c) After equilibrium is reached [2NO 2 (g) ⇌ N 2 O 4 (g)], the color remains the same. Source: Ken O’Donogue

5. Copyright © Houghton Mifflin Company.All rights reserved. 16–5 Figure 16.2: Visualizing the reaction 2BrNO(g) → 2NO(g) + Br 2 (g).

6. Figure 16.3: When molecules collide, a certain minimum energy called the activation energy (E a ) is needed for a reaction to occur.

7. Figure 16.4: Comparison of the activation energies for an uncatalyzed reaction ( E a ) and for the same reaction with a catalyst present ( E’ a ).

8. Copyright © Houghton Mifflin Company.All rights reserved. 16–8 Cutaways of catalytic converters used in automobiles. Source: Delphi Automotive Services

9. An Amana refrigerator, one of many appliances that now use HFC - 134a. This compound is replacing CFCs, which lead to the destruction of the atmospheric ozone.

10. Figure 16.5: A photo showing the ozone “hole” over Antarctica. Source: AP Photo/NOAA

11. Copyright © Houghton Mifflin Company.All rights reserved. 16–11 Figure 16.6: The establishment of the equilibrium vapor pressure over a liquid in a closed container.

12. Copyright © Houghton Mifflin Company.All rights reserved. 16–12 Figure 16.7: The reaction of H 2 O and CO to form CO 2 and H 2 as time passes.

13. Copyright © Houghton Mifflin Company.All rights reserved. 16–13 Figure 16.8: The changes with time in the rates of the forward and reverse reactions for H 2 O(g) + CO(g) ⇌ H 2 (g) + CO 2 (g) when equal numbers of moles of H 2 O(g) and CO(g) are mixed.

14. Copyright © Houghton Mifflin Company.All rights reserved. 16–14

15. Copyright © Houghton Mifflin Company.All rights reserved. 16–15 Spruce needles turned brown by acid rain. Source: Jenny Hager/The Image Works

16. Copyright © Houghton Mifflin Company.All rights reserved. 16–16 As solid copper (II) sulfate pentahydrate, CuSO 4 5H 2 O is heated, it loses H 2 O, eventually forming white CuSO 4.

17. Copyright © Houghton Mifflin Company.All rights reserved. 16–17 Figure 16.9: (a) The initial equilibrium mixture of N 2, H 2, and NH 3. (b) Addition of N 2. (c) The new equilibrium position for the system containing more N 2 (because of the addition of N 2 ), less H 2, and more NH 3 than in (a).

18. Copyright © Houghton Mifflin Company.All rights reserved. 16–18 When blue anhydrous CoCL 2 reacts with water, pink CoCl 2 6H 2 O is formed.

19. Copyright © Houghton Mifflin Company.All rights reserved. 16–19 Figure 16.10: The reaction system : CaCO 3 (s) ⇌ CaO(s) 1 CO 2 (g).

20. Copyright © Houghton Mifflin Company.All rights reserved. 16–20 Figure 16.11: (a) A mixture of NH 3 (g), N 2 (g), and H 2 (g) at equilibrium. (b) The volume is suddenly decreased. (c) The new equilibrium position for the system containing more NH 3 and less N 2 and H 2.

21. Copyright © Houghton Mifflin Company.All rights reserved. 16–21

22. Copyright © Houghton Mifflin Company.All rights reserved. 16–22 Figure 16.12: Shifting the N 2 O 4 (g) ⇌ 2NO 2 (g) equilibrium by changing the temperature.

23. Copyright © Houghton Mifflin Company.All rights reserved. 16–23 Toothpastes containing sodium floride, an additive that helps prevent tooth decay.

24. This X ray of the large intestine has been enhanced by the patient's consumption of barium sulfate. Source: Science Photo Library/Photo Researchers, Inc.