CH9 Zumdahl Thermochem 2008 for Web

CH9 Zumdahl Thermochem 2008 for Web - Chapter 9...

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Chapter 9 Thermodynamics: The First Law Work/Heat E = q + w = heat + work Reaction Enthalpies 1
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Combustion of Gasoline 2C 8 H 18 (l) + 25O 2 (g) 18H 2 O (l) + 16CO 2 (g) H rxn = -1.09 x 10 4 kJ 5,450 kJ of energy released per mole of octane Combustion of 1 gallon of gas 136 MJ energy 2
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Energy: capacity to do work or to produce heat Kinetic energy: motion of object, ½ mv 2 Potential energy: due to position or composition (bonds, height of a mass) Ex. Combustion of methane (CH 4 ): potential energy stored in bonds is converted to kinetic energy (thermal energy) via heat 3
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CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) H rxn = -890 kJ 4
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CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) H rxn = -890 kJ 5 Combustion of methane releases energy
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N 2 (g) + O 2 (g) + energy 2NO(g) endothermic 6
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H 2 O(s) + 6.02 kJ H 2 O(l) Melting of ice 7
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First law of thermodynamics: The total energy of the universe is constant. Also known as “Law of Conservation of Energy”: energy is neither created nor destroyed in ordinary chemical reactions Energy in Joules 8
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A “system” Ex. System is a reaction mixture Surroundings = atmosphere around the reaction mixture 9
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The internal energy of a system E is the sum of kinetic and potential energies of all particles. The internal energy is the capacity of a system to do work; its total store of energy. E = q + w q is heat w is work Energy: Heat + Work 10
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Exothermic versus Endothermic 11
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Work Work: change in energy when an object is moved through a distance Example of work: compression or expansion of a gas W = -P ex V 12
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Varieties of Work 13
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A system doing work (i.e. expansion of a gas). Work is proportional to the external pressure and change in volume. 14
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w = -P V system In (b), the gas has expanded. The system has done work (-w). 15
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A gas in a cylinder of an engine expands by 500.0 mL against a pressure of 1.20 atm. How much work is done? 16
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A balloon is inflated by heating the air inside it. The volume changes from 4.00 x 10 6 L to 4.50 x 10 6 L by addition of 1.3 x 10 8 J of energy as heat at 1 atm. Calculate E. A car engine does 520. kJ of work and loses 220 kJ. of heat. What is the change in energy of the engine?
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