Chapter 7 notes - Chapter 7 Thermochemistry Energy Thermal...

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1 Chapter 7: Thermochemistry Energy & Thermal Chemistry Themes: Energy – Fueling our Bodies Energy - Fueling our World 1 Things We Burn Combustion or burning is a complex sequence of exothermic chemical reactions between a fue and an oxidan a fuel and an oxidant . – Rapid Combustion: accompanied by the production of heat or both heat and light in the form of either a glow or flames. 2
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2 Global Energy Sources Oil Coal Gas Nuclear Fossil Fuels Tera-Watts 3 In 2004, the worldwide energy consumption of the human race was on average 15 TW (= 1.5 x 10 13 W) with 86.5% from burning fossil fuels. Hydro Years (1965-2005) Refer to Ch. 7-9, pg 257-263 The Energy We Get from Fuels • Comparing Heats of Combustion: Fuel kJ/g Hydrogen -150.0 Natural Gas -49.5 Gasoline -47.8 Coal -28.3 Methanol -22.7 Cellulose -17.5 Fossil Fuels 4 • The higher the heat of combustion, the better the fuel! • What is Heat of Combustion? • Where does the energy stored in these fuels come from? Municipal waste -12.7
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3 Capturing Energy from the Sun • Photosynthesis is an ENDOTHERMIC process • Sunlight (energy) is used to build glucose and other simple sugars “A leaf is an amazingly cheap and efficient solar cell.” 5 6CO 2 + 6H 2 O C 6 H 12 O 6 (s) + 6O 2 (g) Chlorophyll Sunlight ⎯⎯⎯⎯→ Utilizing the Captured Energy • Plants – as food – fueling respiration • Energy is extracted by combustion of the plant material •Fossil Fuels –fueling homes & cars 6 • Recall: 6CO 2 + 6H 2 O C 6 H 12 O 6 (s) + 6O 2 (g) Chlorophyll Sunlight 3 2.8 10 / o Hk J m o l Δ =+ ×
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4 Issues with Burning Fossil Fuels • Non-renewable – Plant Matter, aged >300 million years! • Contributions to Global Warming –Ne t CO 2 increase in atmosphere 7 Burning Fossil Fuels – CO 2 Emissions Tonnes Per Capita 8
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5 System versus Surroundings Open System: material & energy exchange Closed System: only Energy exchange Isolated system: 9 Neither material nor energy exchange Refer to Ch. 7-1, pg 226-227 Energy • Energy = the capacity to do work • Potential Energy: • Kinetic Energy: 10 • Thermal Energy? Refer to Ch. 7-1, pg 226-227
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6 Heat • Thermodynamics: The study of heat and its transformations • Thermochemistry: The branch of thermodynamics, as it relates to chemical reactions 11 • Heat (q): energy transferred between a system and its surroundings as a result of a temperature gradient Refer to Ch. 7-2, pg 228-231 Heat Capacity • Heat Capacity (C): the amount of heat required to change the temperature of a system by one degree (J. o C -1 ) or (J. K -1 ) ic Heat in J/g 12 Refer to Ch. 7-2, pg 228-231 Specif
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7 Defining a System’s Capacity to Store Heat q = m x specific heat x Δ T = C x Δ T • Heat Capacity (C) = the quantity of heat (q) required to change the temperature of a “system” by one degree •Specific Heat Capacity = “system” is one gram 13 of material • Molar Heat Capacity = “system” is one mole of material Refer to Ch. 7-2, pg 228-231 Origin of Heat Capacity http://en.wikipedia.org/wiki/Image:Thermally_Agitated_Molecule.gif • Thermal energy is expressed as Thermal energy is expressed as a molecule’s internal motions.
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This note was uploaded on 01/16/2010 for the course CHEMISTRY 1A03 taught by Professor Dr.p.lock during the Fall '08 term at McMaster University.

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Chapter 7 notes - Chapter 7 Thermochemistry Energy Thermal...

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