Chapter6_Thermochemistry

Chapter6_Thermochemi - Chapter 6 Thermochemistry 1 Energy The ability to do work or transfer heat Work Energy transferred when an object is moved

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Chapter 6 Thermochemistry 1
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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
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Units of Energy The SI unit of energy is the joule (J). An older, non-SI unit is still in widespread use: The calorie (cal). 1 cal = 4.184 J 1 food C alorie = 1,000 calorie . 1 J = 1  3
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Potential Energy 4 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
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Kinetic Energy Kinetic energy is energy of motion or energy that is being transferred thermal energy is kinetic 1 2 KE = mv 5
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Tro, Chemistry: A Molecular Approach 6 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 potential energy in the nucleus of atoms Chemical potential energy in the attachment of atoms or because of their position
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System and Surroundings The system includes the part of the universe we want to study. The surroundings are everything else in the universe. system 7
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First Law of Thermodynamics The law of conservation of energy Energy is neither created nor destroyed. 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. Use Fig. 5.5 8
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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
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Tro, Chemistry: A Molecular Approach 10 State Function
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Internal Energy 2200 E depends only on E initial and E final . 2200 E = E final - E initial Use Fig. 5.5 11
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Changes in Internal Energy If E > 0, E final > E initial Therefore, the system absorbed energy from the surroundings. 12
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Changes in Internal Energy If E < 0, E final < E initial Therefore, the system released energy to the surroundings. 13
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Exam 1 Summary
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Tro, Chemistry: A Molecular Approach 15 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 w (work) system gains energy from work + system releases energy by doing work E system gains energy + system releases energy
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System and Surroundings When heat is absorbed by the system from the surroundings, the process is endothermic . 16
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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_Thermochemi - Chapter 6 Thermochemistry 1 Energy The ability to do work or transfer heat Work Energy transferred when an object is moved

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