Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 2 Matter and Energy 2.7 Changes of State 1 When a gram of steam condenses, 2260 J are released.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 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 A solid requires heat to change to a liquid; a liquid gives off heat to change to a solid. 2

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculations Using Heat of Fusion The heat of fusion is the amount of heat released when 1 g of liquid freezes (at its freezing point) is the amount of heat needed to melt 1 g of solid (at its melting point) for water (at 0  C) is 80. cal or 334 J 1 g H 2 O 1 g H 2 O 3 Sublimation and deposition are reversible processes.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculations Using Heat of Fusion 4

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. How many kilojoules are released when 25.0 g of water at 0  C freezes? A kJ B. 0 kJ C kJ Learning Check 5

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. How many kilojoules are released when 25.0 g of water at 0  C freezes? Step 1 List the grams of substance and change of state. Given: 25.0 g of H 2 O(l) Need: number of kilojoules to freeze to H 2 O(s) Step 2 Write the plan to convert grams to heat. grams of H 2 O(l) kilojoules (to freeze) Solution 6

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Step 3 Write the heat conversion factors and metric factors if needed. 1 g of H 2 O(l s) = 334 J 334 J and 1 g H 2 O 1 g H 2 O 334 J 1 kJ = 1000 J 1 kJ and 1000 J 1000 J 1 kJ Solution (continued) 7

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Step 4 Set up the problem with factors. Heat lost to freeze water at 0  C 25.0 g H 2 O x 334 J x 1 kJ = 8.35 kJ 1 g H 2 O 1000 J The answer is C, 8.35 kJ. Solution (continued) 8

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 9 How many joules are needed to melt 15.0 g of ice at 0  C? A. 1,200 J B. 5,010 J C. 96,000 J Learning Check 9

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 10 Step 1 List the grams of substance and change of state. Given: 15.0 g of H 2 O(s) Need: number of joules to melt ice to H 2 O(l) Step 2 Write the plan to convert grams to heat. grams of ice H 2 O(s) joules (to melt) Solution 10

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 11 Step 3 Write the heat conversion factors and metric factor if needed. 1 g of H 2 O(s l) = 334 J 334 J and 1 g H 2 O g of H 2 O 334 J Step 4 Set up the problem with factors. Heat to melt ice at 0  C 15.0 g ice x 334 J = 5010 J 1 g ice The answer is B, 5010 J. Solution (continued) 11

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 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. 12 During evaporation, molecules of the liquid are converted to gas at the surface of the liquid.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Boiling of Water When water is boiling, all the water molecules acquire enough energy to form a gas (vaporize) bubbles of water vapor appear throughout the liquid 13 During boiling, molecules of the liquid are converted to gas throughout the liquid as well as at the surface.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Heat of Vaporization The heat of vaporization is the amount of heat absorbed to change 1 g of liquid to gas at the boiling point released when 1 g of gas changes to liquid at the boiling point Boiling Point of Water = 100  C Heat of Vaporization (water) 540 cal or 2260 cal 1 g H 2 O 14 Vaporization and condensation are reversible processes.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculations Using Heat of Vaporization 15

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100  C? A.113 kJ B.2,260 kJ C.113,000 kJ 16

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100  C? Step 1 List the grams of substance and change of state. Given: 50.0 g of H 2 O(g) Need: number of kilojoules to condense steam to H 2 O(l) Step 2 Write the plan to convert grams to heat. grams of H 2 O(g) kilojoules (to condense) 17

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution (continued) Step 3 Write the heat conversion factors and metric factors if needed. 1 g of H 2 O(g l) = 2260 J 2260 J and 1 g H 2 O 1 g H 2 O 2260 J 1 kJ = 1000 J 1 kJ and 1000 J 1000 J 1 kJ 18

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Step 4 Set up the problem with factors. Heat released when H 2 O(g) condenses at 100  C is: 50.0 g H 2 O x 2260 J x 1 kJ = 113 kJ 1 g H 2 O 1000 J The answer is A. 19

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Sublimation occurs when a solid changes directly 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 Heat of Sublimation (water) 620. cal or 2590 cal 1 g H 2 O 20 Dry ice sublimes at –78 °C.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Summary of Changes of State 21 A solid melts to form a liquid and sublimes to form a gas; a liquid boils to form a gas and freezes to form a solid; a gas condenses to form a liquid and undergoes deposition to form a solid.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Heating Curve 22 On a heating curve, diagonal lines indicate changes in temperature for a state, and horizontal lines (plateaus) indicate changes of state. FIGURE 2.10 (a) A heating curve diagrams changes in state as temperature increases. (b) A cooling curve for water diagrams changes in state as temperature decreases.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 1. A plateau (horizontal line) on a heating curve represents A. a temperature change B. a constant temperature C. a change of state 2. A sloped line on a heating curve represents A. a temperature change B. a constant temperature C. a change of state 23

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 1. A flat line on a heating curve represents B. a constant temperature C. a change of state 2. A sloped line on a heating curve represents A. a temperature change 24

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 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 25 On a cooling curve, diagonal lines indicate changes in temperature for a state, and horizontal lines (plateaus) indicate changes of state. A cooling curve for water diagrams changes in state as temperature decreases.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Use the cooling curve for water to answer each of the following: 1. Water condenses at a temperature of A. 0  CB. 50  CC. 100  C 2. At a temperature of 0  C, liquid water A. freezesB. meltsC. changes to a gas 3. At 40  C, water is a A. solid B. liquidC. gas 4. When water freezes, heat is A. removedB. added 26

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Use the cooling curve for water to answer each of the following: 1. Water condenses at a temperature of C. 100  C 2. At a temperature of 0  C, liquid water A. freezes 3. At 40  C, water is a B. liquid 4. When water freezes, heat is A. removed 27

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Combined Heat Calculations 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 List the grams of substance and change of state. Given: 250. g of ice H 2 O(s); H 2 O(l) water at 37.0  Need: joules to melt H 2 O(s) at 0  C and warm to 37.0  C 37  C  T = 37.0  C – 0  C = 37.0  C temperature increase 0  C solid liquid melting 28

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Combined Heat Calculations (continued) Step 2 Write the plan to convert grams to heat and desired unit g ice x 80. cal = 20,000 cal (2.0 x 10 3 cal) 1 g ice Step 3 Calculate the heat to warm the water from 0  C to 37.0  C g x 37.0  C x 1.00 cal = 9,250 cal g  C Total: Add Step 2 and Step 3 = 29,000 cal (rounded off to 1000s place ) 29

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 30 Learning Check When a volcano erupts, 175 g of steam at 100  C is released. How many kilojoules are lost when the steam condenses, then freezes, at 0  C ? A. 396 kJ B. 528 kJ C. 133 kJ

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 31 Solution Step 1 List the grams of substance and change of state. Given: 175. g of steam H 2 O(g); to H 2 O(s) at 0  C Need: kilojoules to condense H 2 O(g) at 100  C; cool to 0  C, and freeze at 0  C

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 32 Solution Step 2 Write the plan to convert grams to heat and desired unit. Total heat = joules to condense steam at 100  C, cool water to 0  C, freeze water at 0  C, cool ice to –5  C For several changes, we draw a cooling diagram. at 100  C (condensing) 100  C to 0  C (cooling) at 0  C (freezing)

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution (continued) Step 3 Write the heat conversion factors needed. 1 g of H 2 O(l s) = 334 J 334 J and 1 g H 2 O 1 g H 2 O 334 J 1 g of H 2 O(g l) = 2260 J 2260 J and 1 g H 2 O 1 g H 2 O 2260 J SH of H 2 O(l) = J/g  C J and g  C g  C J 33

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 34 Solution (continued) Step 4 Set up problem with factors. Steam condenses at 100  C 175 g x 2260 J x 1 kJ = 396 kJ g 1000 J Water cools from 100  C to 0  C 175 g x 100  C x J x 1 kJ = 73.2 kJ g  C 1000 J Water freezes to ice at 0  C: 175 g x 334 J x 1 kJ = kJ g 1000 J 528 kJ Answer is B, 528 kJ.