chap5yp - C HAPTERS Energy & Chemical Reactions E...

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CHAPTERS Energy & Chemical Reactions I. Energy: Some Basic Principles II. The First Law of Thermodynamics III. Enthalpy Changes for Chemical Reactions IV. Specific Heat Capacity and Calorimetry V. Standard Enthalpy of Formation & Reaction. I. Energy: Some Basic Principles A. Definitions 1. Energy is defined as the capacity to do work or transfer heat. 2. Kinetic energy is the energy associated with an object by virtue of its motion. 3. Potential energy is the energy an object has by virtue of its position in a field of force.
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B. Units of Energy 1. The units of energy can be deduced from the definition of kinetic energy. 2. An object of mass m, moving at a velocity V, has a kinetic energy KE given by: 3. 81 unit of energy is kg m 2 /s 2 , and is defined as the joule (J). 4. A second unit of energy is the calorie (cal), originally defined as the amount of energy required to raise the temperature of 1 g of water by 1 ac. 5. The dietary Calorie (Cal) is used to represent the energy content of foods. James Joule 1818-1889 6. All packaged foods must have labels specifying nutritional values, with energy given in Calories. Nutrition Facts ~s. .e (2lIg) S;rzPttC<lrMl*-" ............... ,.... CeIoMo '20 ........ ~F.~ ,,~---. 1\II1II . ..." sw-dF.Ul5p "' 4'Jlo ~f'Ulq ~FtlI!! 1'loW~'" J"4 ea-.-lllm!! 2'l> ....... ,1!5mQ <ft ~FW~IIWI're :zo:. &lQ!I7q .......... a;, <""1> The label on a cereal box indicates that one serving (With skim milk) "'n provides 250 Cal. What is this energy in kilojoules (kJ) ? 2
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f A good pitcher can throw a baseball so that it travels >J between 60 and 80 miles per hour. A regulation baseball weighing 143 g travels 75 miles per hour (33.5 m/s). What is the kinetic energy of this baseball in joules? In calories? c. Temperature and Heat 1. Almost all chemical reactions absorb or release energy in the form of heat. 2. Heat is defined as the energy that flows into or out of a system because of a difference in temperature between the system and its surroundings. 3. Heat flows fronl a region of higher temperature to one of lower temperature; once the telTlperature becomes equal, heat flow stops. 3
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D. System and Surroundings 1. The system is the specific part of the universe that is of interest in the study. 2. The surroundings is part of the universe that interacts with the system. Water v.apor i1 / , ~ Hcat -+-;-- , ( ± ; HCal I ! l open system closed system isolated system E. Types of Reactions 1. Exothermic process: 2. Endothermic process: 4
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~ ::: '" w 1.1 2H 2 (g) + ~(g) I Exothermic: heal. given off by the system to dIe surroundings 2H 2 O(1) "- Exothermic :>-. e. 1J ~ d:l -r 2Hg(/) + °2(g) f - - _.~ Endothermic: heat ~Ibsorbed by the system from the surroundings 2H O( ) Endothermic I1E = q + W II. The First Law of Thermodynamics A. Introduction 1. The First Law of Thermodynamics states that energy can be converted from ane farm to another, but cannot be created ar destroyed. b.-E
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This note was uploaded on 03/02/2010 for the course CHEM 210 taught by Professor Paukstelis during the Spring '09 term at Kansas State University.

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chap5yp - C HAPTERS Energy &amp; Chemical Reactions E...

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