Lecture Slides on Energy and Matter - Survey of Chemistry I | CHEM 1151K, Study notes of Chemistry

Download Lecture Slides on Energy and Matter - Survey of Chemistry I | CHEM 1151K and more Study notes Chemistry in PDF only on Docsity! 1 Chapter 2 Energy and Matter 2.7 Changes of State General, Organic, and Biological Chemistry 2 Melting and Freezing A substance  is melting when it changes from a solid to a liquid  is freezing when it changes from a liquid to a solid  such as water has a freezing (melting) point of 0 °C General, Organic, and Biological Chemistry 5 Calculations Using Heat of Fusion How much heat in calories is needed to melt 15.0 g of ice at 0 °C ? Given: 15.0 g of water(s) change of state: melting at 0 °C Plan: g of water(s) g of water(l) Write conversion factors: 1 g of water = 80 cal 1 g of water and 80 cal 80 cal 1 g of water General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6 Calculation Using Heat of Fusion Set up the problem to calculate calories: 15.0 g water x 80 cal = 1200 cal 1 g water General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7 Learning Check How many joules are released when 25.0 g of water at 0 °C freezes? 1) 334 J 2) 2000 J 3) 8350 J General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10 Sublimation 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 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11 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 General, Organic, and Biological Chemistry 12 Boiling At boiling,  water molecules acquire the energy to form a gas  bubbles appear throughout the liquid General, Organic, and Biological Chemistry 15 Learning Check How many kilocalories (kcal) are released when 50.0 g of water(g) as steam from a volcano condenses at 100 °C? 1) 27 kcal 2) 540 kcal 3) 2700 kcal General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 16 Solution 1) 27 kcal Given: 50.0 g of water(g) = 50.0 g of water(l) Change of state: water condensing at 100 °C Plan: g of water(g) g of water(l) Write conversion factors: 1 g of water = 540 cal 1 g of water and 540 cal 540 cal 1 g of water 1 kcal = 1000 cal 1 kcal and 1000 cal 1000 cal 1 kcal General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 17 Solution (continued) Set up the problem to calculate kilocalories: 50.0 g water x 540 cal x 1 kcal = 27 kcal 1 g water 1000 cal General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 20 Learning Check A. A plateau (horizontal 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 General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 21 Solution A. A plateau (horizontal line) on a heating curve represents 2) a constant temperature 3) a change of state B. A sloped line on a heating curve represents 1) a temperature change General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 22 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 (horizontal lines) to indicate a change of state General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 25 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? Given: 250 g ice changes to water at 37.0 °C Need: calories to melt at 0 °C and warm to 37.0 °C T = 37.0 °C – 0 °C = 37.0 °C 37.0 °C 0 °C General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 26 Combined Heat Calculations (continued) Conversion factors: 1 g of water (0 °C) = 80 cal 1 g of water (0 °C) and 80 cal 80 cal 1 g of water (0 °C) 1 g of water(l) = 1.00 cal/g °C 1 g of water(l) and 1.00 cal/g °C 1.00 cal/g °C 1 g of water(l) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 27 Combined Heat Calculations (continued) Set up problem: (1) Heat to melt ice (fusion) 250 g ice x 80 cal = 20 000 cal 1 g ice (2) Heat the water(l) from 0 °C to 37.0 °C 250 g x 37.0 °C x 1.00 cal = 9250 cal g °C Total: 20 000 cal + 9250 cal = 29 000 cal (rounded) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.