Chapter6_Thermochemistry

Chapter6_Thermochemistry - Chapter 6 y Thermochemistry...

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1 Chapter 6 Thermochemistry 1 Energy • The ability to do work or transfer heat. Work : Energy transferred when an object is moved by force. Heat : Energy transferred as a result of difference in temperature. 2 Units of Energy he SI unit of energy is the ule (J) • The SI unit of energy is the joule (J). • An older, non-SI unit is still in widespread use: The calorie (cal). 1 J = 1  kg m 2 s 2 1 cal = 4.184 J • 1 food C alorie = 1,000 calorie . 3 Potential Energy Potential energy is energy that is stored in an object, or energy associated with the composition and position of the object energy stored in the structure of a compound is potential 4
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2 Kinetic Energy Kinetic energy is energy of motion or nergy that is being transferred energy that is being transferred thermal energy is kinetic 1 2 KE = mv 2 5 Some Forms of Energy • Electrical kinetic energy associated with the flow of electrical charge • Heat or Thermal Energy kinetic energy associated with molecular motion • Light or Radiant Energy kinetic energy associated with energy transitions in an atom • Nuclear otential energy in the nucleus of atoms Tro, Chemistry: A Molecular Approach 6 potential energy in the nucleus of atoms • Chemical potential energy in the attachment of atoms or because of their position System and Surroundings he ystem cludes • The system includes the part of the universe we want to study. • The surroundings are everything else in the niverse. universe. system 7 First Law of Thermodynamics • The law of conservation of energy • Energy is neither created nor destroyed. gy y • In other words, the total energy of the universe is a constant; if the system loses energy, it must be gained by the surroundings, and vice versa. se Fig 5 5 Use Fig. 5.5 8
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3 Internal Energy • The internal energy of a system is the sum of all kinetic and potential energies of all components of the system; we call it E. • Usually we have no way of knowing the internal energy of a system; finding that value is simply too complex a problem. • However, we do know that the internal energy of a system is a state function. 9 State Function Tro, Chemistry: A Molecular Approach 10 Internal Energy ± E depends only on E initial and E final . E = E nal - E itial final initial se Fig 5 5 Use Fig. 5.5 11 Changes in Internal Energy • If E > 0, E final > E initial Therefore, the system absorbed energy from the surroundings. 12
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4 Changes in Internal Energy • If E < 0, E final < E initial Therefore, the system released energy to the surroundings. 13 How Is Energy Exchanged? • energy is exchanged between the system and surroundings through heat and work q = heat (thermal) energy w = work energy q and w are NOT state functions, their value depends on the process E = q + w q (heat) system gains heat energy + system releases heat energy Tro, Chemistry: A Molecular Approach 14 w (work)
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This note was uploaded on 09/14/2009 for the course CHEM 105 taught by Professor Zhao during the Summer '08 term at IUPUI.

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Chapter6_Thermochemistry - Chapter 6 y Thermochemistry...

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