End Show © Copyright Pearson Prentice Hall Slide 1 of 34 The Flow of Energy—Heat and Work The temperature of lava from a volcano ranges from 550°C to 1400°C. As lava flows, it loses heat and begins to cool. You will learn about heat flow and why some substances cool down or heat up more quickly than others In what direction does heat flow?

End Show Slide 2 of 34 © Copyright Pearson Prentice Hall > The Flow of Energy—Heat and Work Energy Transformations Heat, represented by q, is energy that transfers from one object to another because of a temperature difference between them. Heat always flows from a warmer object to a cooler object. 17.1

Energy Transformations Thermochemistry is the study of energy changes that occur during chemical reactions and changes in state. The energy stored in the chemical bonds of a substance is called chemical potential energy When fuel is burned in a car engine, chemical potential energy is released and is used to do work.

What happens in endothermic and exothermic processes? In an endothermic process, the system gains heat as the surroundings cool down. An endothermic process is one that absorbs heat from the surroundings. In an exothermic process, the system loses heat as the surroundings heat up. An exothermic process is one that releases heat to its surroundings. The law of conservation of energy states that in any chemical or physical process, energy is neither created nor destroyed. 17.1

© Copyright Pearson Prentice Hall Slide 5 of 34 End Show Conceptual Problem 17.1

© Copyright Pearson Prentice Hall Slide 6 of 34 End Show Practice Problems for Conceptual Problem 17.1

End Show © Copyright Pearson Prentice Hall The Flow of Energy—Heat and Work > Slide 7 of 34 Units for Measuring Heat Flow 17.1 Heat flow is measured in two common units, the calorie and the joule. (1 calorie = Joules) Heat (q) can be calculated using the mass of substance, the specific heat capacity (C) of the substance, and the change in temperature (T f -T i )

End Show Slide 8 of 34 © Copyright Pearson Prentice Hall > The Flow of Energy—Heat and Work Heat Capacity and Specific Heat Specific Heat Capacity (Note: symbol is C ; not o C) The specific heat capacity, or simply the specific heat, of a substance is the amount of heat it takes to raise the temperature of 1 g of the substance 1 degree Celcius. 17.1

End Show Slide 9 of 34 © Copyright Pearson Prentice Hall > The Flow of Energy—Heat and Work Heat Capacity and Specific Heat 17.1

© Copyright Pearson Prentice Hall SAMPLE PROBLEM Slide 11 of 34 End Show 17.1

End Show © Copyright Pearson Prentice Hall Slide 12 of 34 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 17.1 Section Quiz. 17.1

© Copyright Pearson Prentice Hall Slide 13 of 34 End Show 1. The energy released when a piece of wood is burned has been stored in the wood as a.sunlight. b.heat. c.calories. d.chemical potential energy Section Quiz.

© Copyright Pearson Prentice Hall Slide 14 of 34 End Show 2. Which of the following statements about heat is false? a.Heat is the same as temperature. b.Heat always flows from warmer objects to cooler objects. c.Adding heat can cause an increase in the temperature of an object. d.Heat cannot be specifically detected by senses or instruments Section Quiz.

© Copyright Pearson Prentice Hall Slide 15 of 34 End Show 3. Choose the correct words for the spaces: In an endothermic process, the system ________ heat when heat is ________ its surroundings, so the surroundings _____________. a.gains, absorbed from, cool down. b.loses, released to, heat up. c.gains, absorbed from, heat up. d.loses, released to, cool down Section Quiz.

© Copyright Pearson Prentice Hall Slide 16 of 34 End Show 5. Assuming that two samples of different materials have equal mass, the one that becomes hotter from a given amount of heat is the one that a.has the higher specific heat capacity. b.has the higher molecular mass. c.has the lower specific heat capacity. d.has the higher density Section Quiz.

© Copyright Pearson Prentice Hall Slide 17 of 34 End Show Calorimetry Calorimetry is the precise measurement of the heat flow into or out of a system for chemical and physical processes. In calorimetry, the heat released by the system is equal to the heat absorbed by its surroundings. Conversely, the heat absorbed by a system is equal to the heat released by its surroundings. 17.2

© Copyright Pearson Prentice Hall Slide 18 of 34 End Show Calorimetry Constant-Volume Calorimeters a.Calorimetry experiments can be performed at a constant volume using a bomb calorimeter. 17.2

Calorimetry The insulated device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter (constant-pressure calorimeter) The heat content of a system at constant pressure is the same as a property called the enthalpy (H) of the system. (We will use this coffee cup calorimeter in lab.) 17.2

© Copyright Pearson Prentice Hall Slide 20 of 34 End Show for Sample Problem 17.2

© Copyright Pearson Prentice Hall Slide 21 of 34 End Show 17.2

© Copyright Pearson Prentice Hall Slide 22 of 34 End Show 17.2

© Copyright Pearson Prentice Hall Slide 23 of 34 End Show 17.2

© Copyright Pearson Prentice Hall Slide 24 of 34 End Show 17.2

© Copyright Pearson Prentice Hall Slide 25 of 34 End Show How can you express the enthalpy change for a reaction in a chemical equation? In a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product. A chemical equation that includes the enthalpy change is called a thermochemical equation. CaO (s) + H 2 O (l) → Ca(OH) 2 (s) + heat 17.2 Thermochemical Equations

© Copyright Pearson Prentice Hall Slide 26 of 34 End Show Thermochemical Equations A chemical equation that includes the enthalpy change is called a thermochemical equation. The heat of reaction is the enthalpy change for the chemical equation exactly as it is written. 17.2

© Copyright Pearson Prentice Hall Slide 27 of 34 End Show Thermochemical Equations 17.2 Exothermic Reaction

© Copyright Pearson Prentice Hall Slide 28 of 34 End Show Thermochemical Equations 17.2 Endothermic Reaction

© Copyright Pearson Prentice Hall Slide 29 of 34 End Show 17.3

© Copyright Pearson Prentice Hall Slide 31 of 34 End Show for Sample Problem 17.3

© Copyright Pearson Prentice Hall Slide 32 of 34 End Show Thermochemical Equations The heat of combustion is the heat of reaction for the complete burning of one mole of a substance. (See reference Table I) 17.2

© Copyright Pearson Prentice Hall Slide 33 of 34 End Show 17.2 Section Quiz. 2. For the reaction CaO(s) + H2O(l)  Ca(OH) 2 (s),  H =  65.2 kJ. This means that 62.5 kJ of heat is __________ during the process. a.absorbed b.destroyed c.changed to mass d.released

© Copyright Pearson Prentice Hall Slide 34 of 34 End Show 17.2 Section Quiz. 3.How much heat is absorbed by 325 g of water if its temperature changes from 17.0°C to 43.5°C? The specific heat of water is 4.18 J/g°C. a.2.00 kJ b.3.60 kJ c.36.0 kJ d.360 kJ

© Copyright Pearson Prentice Hall Slide 35 of 34 End Show 4. Which of the following is a thermochemical equation for an endothermic reaction? a.CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) kJ b kJ + 2H 2 O(l)  2H 2 (g) + O 2 (g) c.CaO(s) + H 2 O(l)  Ca(OH) 2 (s) 65.2 kJ d.2NaHCO 3 (s) 129 kJ  Na 2 CO 3 (s) + H 2 O(g) + CO 2 (g) 17.2 Section Quiz.

© Copyright Pearson Prentice Hall Slide 36 of 34 End Show 5. Oxygen is necessary for releasing energy from glucose in organisms. How many kJ of heat are produced when 2.24 mol glucose reacts with an excess of oxygen? C 6 H 12 O 6 (s) + 6O 2 (g)  6CO 2 (g) + 6H 2 O(g) kJ/mol a.4.66 kJ b.9.31 kJ c.1048 kJ d.6290 kJ 17.2 Section Quiz.