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Chapter 10 Energy

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Chapter 10 Table of Contents Copyright © Cengage Learning. All rights reserved 2 10.1 The Nature of Energy 10.2 Temperature and Heat 10.3 Exothermic and Endothermic Processes 10.4 Thermodynamics 10.5 Measuring Energy Changes 10.6Thermochemistry (Enthalpy) 10.7 Hess’s Law 10.8 Quality Versus Quantity of Energy 10.9 Energy and Our World 10.10Energy as a Driving Force

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Section 10.1 The Nature of Energy Return to TOC Copyright © Cengage Learning. All rights reserved 3 Ability to do work or produce heat. That which is needed to oppose natural attractions. Law of conservation of energy – energy can be converted from one form to another but can be neither created nor destroyed. The total energy content of the universe is constant. Energy

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Section 10.1 The Nature of Energy Return to TOC 4 Potential energy – energy due to position or composition. Kinetic energy – energy due to motion of the object and depends on the mass of the object and its velocity. Energy Telekinesis Video Part 1 Telekinesis Video Part 2

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Section 10.1 The Nature of Energy Return to TOC 5 Types of Energy 1. Kinetic energy 2. Potential energy 3. Chemical energy 4. Heat energy 5. Electric energy 6. Radiant energy Energy Transformations

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Section 10.1 The Nature of Energy Return to TOC 6 In the initial position, ball A has a higher potential energy than ball B. Initial Position

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Section 10.1 The Nature of Energy Return to TOC 7 After A has rolled down the hill, the potential energy lost by A has been converted to random motions of the components of the hill (frictional heating) and to the increase in the potential energy of B. Final Position

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Section 10.1 The Nature of Energy Return to TOC 8 Temperature = average kinetic energy. Heat= total energy. Both of the above are at 70 o F. Which has the most heat?

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Section 10.2 Temperature and Heat Return to TOC Copyright © Cengage Learning. All rights reserved 9 A measure of the random motions of the components of a substance. Temperature

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Section 10.2 Temperature and Heat Return to TOC Copyright © Cengage Learning. All rights reserved 10 A flow of energy between two objects due to a temperature difference between the objects. Heat is the way in which thermal energy is transferred from a hot object to a colder object. Heat

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Section 10.3 Exothermic and Endothermic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 11 Energy Changes Accompanying the Burning of a Match

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Section 10.3 Exothermic and Endothermic Processes Return to TOC 12 Energy Changes and Chemical Reactions 4 C 3 H 5 N 3 O 9 6 N 2 + 10 H 2 O + 12 CO 2 + O 2 + 5720kJ Nitroglycerine Exothermic

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Section 10.3 Exothermic and Endothermic Processes Return to TOC 13 Endothermic Process: Heat flow is into a system. Absorb energy from the surroundings. q = positive(+) Exothermic Process: Energy flows out of the system. q = negative (-) Energy gained by the surroundings must be equal to the energy lost by the system.

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Section 10.3 Exothermic and Endothermic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 14 Concept Check Is the freezing of water an endothermic or exothermic process? Explain.

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Section 10.3 Exothermic and Endothermic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 15 Concept Check Classify each process as exothermic or endothermic. Explain. The system is underlined in each example. a)Your hand gets cold when you touch ice. b)The ice gets warmer when you touch it. c)Water boils in a kettle being heated on a stove. d)Water vapor condenses on a cold pipe. e)Ice cream melts. Exo Endo Exo Endo

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Section 10.3 Exothermic and Endothermic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 16 Concept Check For each of the following, define a system and its surroundings and give the direction of energy transfer. a)Methane is burning in a Bunsen burner in a laboratory. b)Water drops, sitting on your skin after swimming, evaporate. System=burner, surroundings= lab, energy to system System=drops, surroundings= air, energy to surroundings

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Section 10.3 Exothermic and Endothermic Processes Return to TOC Copyright © Cengage Learning. All rights reserved 17 Concept Check Hydrogen gas and oxygen gas react violently to form water. Which is lower in energy: a mixture of hydrogen and oxygen gases, or water? Explain.

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Section 10.4 Thermodynamics Return to TOC 18 Study of energy Law of conservation of energy is often called the first law of thermodynamics. The energy of the universe is constant.

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Section 10.5 Measuring Energy Changes Return to TOC 19 The common energy units for heat are the calorie and the joule. calorie – the amount of energy (heat) required to raise the temperature of one gram of water 1 o C. Joule – 1 calorie = 4.184 joules

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Section 10.5 Measuring Energy Changes Return to TOC 20 Convert 60.1 cal to joules. Example

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Section 10.5 Measuring Energy Changes Return to TOC Copyright © Cengage Learning. All rights reserved 21 1.The amount of substance being heated (number of grams). 2.The temperature change (number of degrees). 3.The identity of the substance. Specific heat capacity is the energy required to change the temperature of a mass of one gram of a substance by one Celsius degree. Energy (Heat) Required to Change the Temperature of a Substance Depends On:

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Section 10.5 Measuring Energy Changes Return to TOC Copyright © Cengage Learning. All rights reserved 22 Specific Heat Capacities of Some Common Substances

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Section 10.5 Measuring Energy Changes Return to TOC Copyright © Cengage Learning. All rights reserved 23 Energy (heat) required, Q = s × m × ΔT Since q=ΔH (change of heat) ΔH = s x m x ΔT Q = energy (heat) required (J) s = specific heat capacity (J/°C·g) m = mass (g) ΔT = change in temperature (°C) To Calculate the Energy Required for a Reaction:

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Section 10.5 Measuring Energy Changes Return to TOC 24 Energy of a Snickers Bar There are 311 Cal in a Snickers Bar. If you added this much heat to a gallon of water at 25 o C what would be the final temperature? 311 Cal = 311,000 cal 311,000 cal = 1.000 cal/g o C x 3960.4g x ? o C 1 gallon of water weighs 3960.4 g Solving for the change of temperature gives us 78.5 o C Add this to the 25 o C to get 104 o C which is above the boiling point of water (100 o C) Heat = SH x m x ΔT

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Section 10.5 Measuring Energy Changes Return to TOC Copyright © Cengage Learning. All rights reserved 25 Calculate the amount of heat energy (in joules) needed to raise the temperature of 6.25 g of water from 21.0°C to 39.0°C. Where are we going? We want to determine the amount of energy needed to increase the temperature of 6.25 g of water from 21.0°C to 39.0°C. What do we know? The mass of water and the temperature increase. Example

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Section 10.5 Measuring Energy Changes Return to TOC Copyright © Cengage Learning. All rights reserved 26 Calculate the amount of heat energy (in joules) needed to raise the temperature of 6.25 g of water from 21.0°C to 39.0°C. What information do we need? We need the specific heat capacity of water. 4.184 J/g°C How do we get there? Example

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Section 10.5 Measuring Energy Changes Return to TOC 27 Exercise A sample of pure iron requires 142 cal of energy to raise its temperature from 23ºC to 92ºC. What is the mass of the sample? (The specific heat capacity of iron is 0.45 J/gºC.) a)0.052 g b)4.6 g c)19 g d)590 g

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Section 10.5 Measuring Energy Changes Return to TOC 28 Concept Check A 100.0 g sample of water at 90.°C is added to a 500.0 g sample of water at 10.°C. The final temperature of the water is: a) Between 50°C and 90°C b) 50°C c) Between 10°C and 50°C Calculate the final temperature of the water. (90 o (100g)+ 10 o (500g))/600g T = 23 o

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Section 10.5 Measuring Energy Changes Return to TOC 29 Concept Check You have a Styrofoam cup with 50.0 g of water at 10. C. You add a 50.0 g iron ball at 90. C to the water. (s H2O = 4.18 J/°C·g and s Fe = 0.45 J/°C·g) The final temperature of the water is: a) Between 50°C and 90°C b) 50°C c) Between 10°C and 50°C Calculate the final temperature of the water. 18°C 50.0g Fe (0.45SH Fe )(90-X o C)=50.0g w (4.18SH w )(X-10 o C)

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 30 Consider the reaction: S(s) + O 2 (g) → SO 2 (g) ΔH = –296 kJ per mole of SO 2 formed. Calculate the quantity of heat released when 2.10 g of sulfur is burned in oxygen at constant pressure. Where are we going? We want to determine ΔH for the reaction of 2.10 g of S with oxygen at constant pressure. What do we know? When 1 mol SO 2 is formed, –296 kJ of energy is released. We have 2.10 g S. Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 31 Consider the reaction: S(s) + O 2 (g) → SO 2 (g) ΔH = –296 kJ per mole of SO 2 formed. Calculate the quantity of heat released when 2.10 g of sulfur is burned in oxygen at constant pressure. How do we get there? Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 32 Exercise Consider the combustion of propane: C 3 H 8 (g) + 5O 2 (g) → 3CO 2 (g) + 4H 2 O(l) ΔH = –2221 kJ Assume that all of the heat comes from the combustion of propane. Calculate ΔH in which 5.00 g of propane is burned in excess oxygen at constant pressure. –252 kJ

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 33 Calorimetry Enthalpy, H is measured using a calorimeter.

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 34 In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 35 This reaction also can be carried out in two distinct steps, with enthalpy changes designated by ΔH 2 and ΔH 3. N 2 (g) + O 2 (g) → 2NO(g) ΔH 2 = 180 kJ 2NO(g) + O 2 (g) → 2NO 2 (g) ΔH 3 = – 112 kJ N 2 (g) + 2O 2 (g) → 2NO 2 (g) ΔH 2 + ΔH 3 = 68 kJ ΔH 1 = ΔH 2 + ΔH 3 = 68 kJ N 2 (g) + 2O 2 (g) → 2NO 2 (g) ΔH 1 = 68 kJ

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 36 If a reaction is reversed, the sign of ΔH is also reversed. The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction. If the coefficients in a balanced reaction are multiplied by an integer, the value of ΔH is multiplied by the same integer. Characteristics of Enthalpy Changes

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 37 Consider the following data: Calculate ΔH for the reaction Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 38 Work backward from the required reaction, using the reactants and products to decide how to manipulate the other given reactions at your disposal. Reverse any reactions as needed to give the required reactants and products. Multiply reactions to give the correct numbers of reactants and products. Problem-Solving Strategy

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 39 Reverse the two reactions: Desired reaction: Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 40 Multiply reactions to give the correct numbers of reactants and products: 4( ) 4( ) 3( ) 3( ) Desired reaction: Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 41 Final reactions: Desired reaction: ΔH = +1268 kJ Example

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 42 Concept Check Calculate ΔH for the reaction: SO 2 + ½O 2 → SO 3 ΔH = ? Given:(1) S + O 2 → SO 2 ΔH = –297 kJ (2) 2S + 3O 2 → 2SO 3 ΔH = –792 kJ a)–693 kJ b)101 kJ c)693 kJ d)–99 kJ Turn the first reaction around and divide the second reaction by 2. Do the same with the ΔH’s. -792/2 + 297 = -99 kJ

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 43 Carbon based molecules from decomposing plants and animals Energy source for United States Fossil Fuels

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 44 Thick liquids composed of mainly hydrocarbons. Hydrocarbon – compound composed of C and H. Petroleum

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 45 Gas composed of hydrocarbons. Natural Gas

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 46 Formed from the remains of plants under high pressure and heat over time. Coal

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 47 Greenhouse Effect Effects of Carbon Dioxide on Climate

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 48 Atmospheric CO 2 Controlled by water cycle Could increase temperature by 10 o C Effects of Carbon Dioxide on Climate

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Global Warming

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Global Warming

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Global Warming

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Global Warming

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 53 Solar Nuclear Biomass Wind Synthetic fuels New Energy Sources

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 54 Natural processes occur in the direction that leads to an increase in the disorder of the universe. Example Consider a gas trapped as shown

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 55 What happens when the valve is opened?

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 56 Energy spread Matter spread Two Driving Forces Gives off energy when solid forms. Spreads out when dissolves.

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 57 In a given process concentrated energy is dispersed widely. This happens in every exothermic process. Energy Spread

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 58 Molecules of a substance spread out to occupy a larger volume. Processes are favored if they involve energy and matter spread. Matter Spread

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 59 Function which keeps track of the tendency for the components of the universe to become disordered. Measure of disorder or randomness Entropy, S

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC Copyright © Cengage Learning. All rights reserved 60 What happens to the disorder in the universe as energy and matter spread? Entropy, S

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Section 10.6 Thermochemistry (Enthalpy) Return to TOC 61 The entropy of the universe is always increasing. Second Law of Thermodynamics The heat death of the universe will occur when all particles of matter ultimately have the same average kinetic energy and exist in a state of maximum disorder. From this To this

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