1. 1 Chapter 2Energy and Matter 2.6 Changes of State Copyright © 2009 by Pearson Education, Inc.

2. 2 Melting and Freezing A substance is melting while it changes from a solid to a liquid. is freezing while it changes from a liquid to a solid. such as water has a freezing (melting) point of 0 °C.

3. 3 Calculations Using Heat of Fusion The heat of fusion is the amount of heat released when 1 gram of liquid freezes (at its freezing point). is the amount of heat needed to melt 1 gram of a solid (at its melting point). for water (at 0 °C) is 80. cal 1 g water

4. 4 The heat needed to freeze (or melt) a specific mass of water (or ice) is calculated using the heat of fusion. Heat = g water (ice) x 80. cal 1 g water (ice) Example: How much heat in cal is needed to melt 15. g of ice? 15. g ice x 80. cal = 1200 cal 1 g ice Calculation Using Heat of Fusion

5. Study Tip: Using Heat of F Fusion 5

6. 6 A. How many calories are needed to melt 5.0 g of ice at 0 °C? 1) 80. cal2) 4.0 x 10 2 cal 3) 0 cal B. How many calories are released when 25 g of water at 0 °C freezes? 1) 80. cal2) 0 cal 3) 2.0 x 10 3 cal Learning Check

7. 7 A. How many calories are needed to melt 5.00 g of ice at 0 °C? 2) 4.0 x 10 2 cal 5.0 g x 80. cal 1 g B. How many calories are released when 25.0 g of water at 0 °C freezes? 3) 2.0 x 10 3 cal 25 g x 80. cal 1 g Solution

8. 8 Sublimation occurs when particles change directly from solid to a gas. is typical of dry ice, which sublimes at -78  C. takes place in frost-free refrigerators. is used to prepare freeze- dried foods for long-term storage. Copyright © 2009 by Pearson Education, Inc.

9. 9 Evaporation and Condensation Water evaporates when molecules on the surface gain sufficient energy to form a gas. condenses when gas molecules lose energy and form a liquid. Copyright © 2009 by Pearson Education, Inc.

10. 10 Boiling At boiling, all the water molecules acquire enough energy to form a gas. bubbles appear throughout the liquid. Copyright © 2009 by Pearson Education, Inc.

11. 11 Heat of Vaporization The heat of vaporization is the amount of heat absorbed to vaporize 1 g of a liquid to gas at the boiling point. released when 1 g of a gas condenses to liquid at the boiling point. Boiling Point of Water = 100 °C Heat of Vaporization (water) = 540 cal 1 g water

12. 12 Learning Check How many kilocalories (kcal) are released when 50.0 g of steam from a volcano condenses at 100 °C? 1) 27 kcal 2) 540 kcal 3) 2700 kcal

13. 13 Solution How many kilocalories (kcal) are released when 50.0 g of steam in a volcano condenses at 100 °C? 1) 27 kcal 50.0 g steam x 540 cal x 1 kcal = 27 kcal 1 g steam 1000 cal

14. 14 Summary of Changes of State

15. 15 Heating Curve A heating curve illustrates the changes of state as a solid is heated. uses sloped lines to show an increase in temperature. uses plateaus (flat lines) to indicate a change of state. Copyright © 2009 by Pearson Education, Inc.

16. 16 A. A flat line on a heating curve represents 1) a temperature change. 2) a constant temperature. 3) a change of state. B. A sloped line on a heating curve represents 1) a temperature change. 2) a constant temperature. 3) a change of state. Learning Check

17. 17 A. A flat line on a heating curve represents 2) a constant temperature. 3) a change of state. (note that this is happening as energy is being put into the system. The energy is being used to change state instead of increase the temperature.) B. A sloped line on a heating curve represents 1) a temperature change. Solution

18. 18 Cooling Curve A cooling curve illustrates the changes of state as a gas is cooled. uses sloped lines to indicate a decrease in temperature. uses plateaus (flat lines) to indicate a change of state. Copyright © 2009 by Pearson Education, Inc.

19. 19 Use the cooling curve for water to answer each. A. Water condenses at a temperature of 1) 0 °C.2) 50 °C.3) 100 °C. B. At a temperature of 0 °C, liquid water 1) freezes.2) melts.3) changes to a gas. C. At 40 °C, water is a 1) solid. 2) liquid.3) gas. D. When water freezes, heat is 1) removed.2) added. Learning Check

20. 20 Use the cooling curve for water to answer each. A. Water condenses at a temperature of 3) 100 °C. B. At a temperature of 0 °C, liquid water 1) freezes. C. At 40 °C, water is a 2) liquid. D. When water freezes, heat is 1) removed. Solution

21. 21 To reduce a fever, an infant is packed in 250. g of ice. If the ice (at 0 °C) melts and warms to body temperature (37.0 °C), how many calories are removed from the body? Step 1: Diagram the changes 37 °C  T = 37.0 °C - 0°C = 37.0 °C temperature increase 0 °C solid liquid melting Combined Heat Calculations

22. 22 Combined Heat Calculations (continued) Step 2: Calculate the heat to melt ice (fusion) 250. g ice x 80. cal= 20 000 cal 1 g ice Step 3: Calculate the heat to warm the water from 0 °C to 37.0 °C 250. g x 37.0 °C x 1.00 cal = 9 250 cal g °C Total: Step 2 + Step 3 = 29 000 cal (rounded to 2 SF)