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Chapter 4: Energy, Chemistry, and Society

Chapter 4: Energy, Chemistry, and Society. What do you think of when you hear the word. ENERGY?. Like the energy of a crowd, You can’t see it, Can’t measure it, But you know it is there. Terms that need to be defined:. Energy is the capacity to do work.

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Chapter 4: Energy, Chemistry, and Society

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  1. Chapter 4: Energy, Chemistry, and Society

  2. What do you think of when you hear the word ENERGY? Like the energy of a crowd, You can’t see it, Can’t measure it, But you know it is there.

  3. Terms that need to be defined: Energy is the capacity to do work. Work is movement against a force (w = f x d). Heat is energy that flows from a hotter to a colder object. Temperature determines the direction of heat flow. Heatis a consequence of motion at the molecular level; temperatureis a measure of the average speed of that motion. 4.2

  4. What are units of heat? The joule (J): 1 J is the amount of energy required to raise a 1-kg object 10 cm against the force of gravity. The calorie (cal): 1 cal is the amount of heat required to raise the temperature of 1 g of water by 1 oC. 1 calorie = 4.184 J 1 kcal = 1000 cal = 1 Cal (1 dietary cal) So that 450 Cal doughnut is really 450,000 calories! 4.2

  5. Diagram of a Power Plant electricity work heat 4.2

  6. Power plants are inevitably inefficient Potential energy (chemical bonds) The First Law of Thermodynamics Energy is neither created nor destroyed, but may be transformed from one form to another. burner Heat energy Taking random, thermal energy and transforming it into ordered work goes against the Second Law of Thermodynamics. gas turbine Mechanical energy Second Law of Thermodynamics – the entropy of the universe is increasing generator Electrical energy 4.2

  7. Bomb calorimeters can be used to determine the heat of combustion If you test a reaction that releases heat, the temperature of the water will increase. 4.3

  8. Hydrocarbon fuels like methane (CH4) burn in the presence of oxygen to produce carbon dioxide and water. Energy is released in this process called combustion. CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l) + ENERGY When energy is released during the course of a chemical reaction, it is said to be an EXOTHERMIC reaction. The combustion of methane gas releases 50.1 kJ/g of CH4 This is the equivalent of 802.3 kJ/mol CH4. 4.3

  9. CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l) Net energy change is - 802.3 kJ/mol CH4 Exothermic reaction The products are lower in energy than the reactants Exothermic reaction: DE is a negative value. 4.3

  10. Activation energy –the energy required to initiate the reaction Molecules must possess enough energy so that their collisions will be productive- leading to products. Exothermic reaction ENDOTHERMIC reactions will have products higher in energy (DE will be positive) than the reactants; there will still be a required activation energy. 4.5

  11. Energy Changes at the Molecular Level The energy changes are due to the rearrangement of the atoms of the reactants and products; it is the breaking and forming of bonds that dictates if a reaction will be endothermic or exothermic. Bond energyis the amount of energy that must be absorbed to break a chemical bond. energy Breaking bonds ALWAYS requires energy! 4.4

  12. 4.4

  13. Consider: 2 H2 + O2 2 H2O Bonds breaking 2 H-H + O=O Bonds forming 4 O-H (2 H-O-H) 4.4

  14. History of U.S. Energy Consumption by Source 1800-2000 1 EJ = 1018 J 4.6

  15. How do Different Fuels Stack Up? High E content and the only product of its combustion is water! 4.6

  16. Petroleum – from where does the U.S. import it? 2003: U.S. consumption was 180 billion gallons. Over 57% of it was imported. The U.S. has 5% of the world’s population, yet consumes 25% of the oil produced worldwide. 4.8

  17. One of the drawbacks to petroleum is that it must be refined before use. 4.8

  18. How do we use each barrel (42 gal) of petroleum? This 1.25 gal includes nonrenewable feedstocks for all plastics, pharmaceuticals, fabrics and other carbon-based products. Over 87% of each barrel is used for transportation and heating. 4.8

  19. Gasoline Additives Elimination of octane enhancing tetraethyl lead (TEL) created a need to find substitutes. MTBE –methyl tertiary-butyl ether Ethanol (ethyl alcohol) Human health effects of exposure to MTBE are not known. 4.10

  20. Fuel Alternatives • Biodiesel fuel use is on the rise. • Made from natural, renewable sources (veg oils, animal fats). • Can be used as pure fuel or blended with petroleum • Ethanol-renewable, but more expensive than gasoline. • Some believe it takes more energy to produce a gallon of ethanol than you will obtain from burning it. • Controversy: National Corn Growers vs. American Petroleum Institute

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