Chapter 4 - Energy Energy Energy, Work and Heat Energy,...

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Unformatted text preview: Energy Energy Energy, Work and Heat Energy, Work - some physical action against a force Lifting a book against gravity Pushing something against friction Stretching a rubber band Energy released in combustion heats gases, the Energy gases expand pushing pistons, resulting in forward motion of a car forward Energy – the capacity to do work Energy, Work and Heat Energy, Heat – energy that flows from a hotter to a Heat colder object colder Temperature a measure of the heat energy in something a statistical measure of the average speed of statistical molecules (higher temp. = faster moving molecules) molecules) Energy, Work and Heat Energy, Units of Energy: Joules Joules 1 Joule = energy needed to lift a 1 kg mass by Joule 10cm against gravity 10cm 1kJ = 1000J 1 calorie = energy needed to raise the temperature calorie of 1g of water by 1°C of 1 calorie = 4.184 J 1kcal = 4.184kJ Calories in food: 1 Calorie = 1kcal = 1000 calories Calories Calories • Energy Transformation Energy 1st Law of Thermodynamics (law of 1st conservation of energy and mass) conservation Energy is neither created nor destroyed It can be transferred (billiard balls) It can be transformed (energy stored in fuel It released as heat) released Energy stored in some way Water at the top of a waterfall A book lifted to a shelf Energy related to the position of atoms and Energy molecular structure and stored in chemical bonds molecular Potential Energy Energy Transformation Energy Kinetic Energy The energy of motion water in a waterfall book falls off shelf – potential energy is converted book to kinetic energy to heat – energy characterized by the motion of heat molecules molecules book hits floor – kinetic energy converted to book thermal energy (book, ground and air will be slightly warmed) slightly Thermal Energy Energy Transformation Energy Fuel to Energy Fuel Combustion combination of fuel and oxygen to form products combination the most common energy generating chemical the reaction reaction CH4 + 2 O2 → CO2 + 2 H2O + energy any chemical or physical change accompanies by any the release of heat the chemical – combustion physical – condensation Exothermic Fuel to Energy Fuel Endothermic any chemical or physical change accompanied by any the absorption of energy the chemical – photosynthesis chemical energy + 6 CO2 + 6 H2O → C6H12O6 + 6 O2 energy chemical – electrolysis of water chemical energy + 2 H2O → 2 H2 + O2 energy Fuel to Energy Fuel Energy change refers to the energy of the system system Fuel to Energy Fuel Energy change in a system showing net energy change only showing net Reactants have more energy than products Energy is released - exothermic Fuel to Energy Fuel In the case of combustion reactions, the energy In combustion the difference is called the heat of combustion heat the quantity of heat energy that is given off when a the specified amount of a substances burns specified usually reported in kJ/mol or kJ/g Fuel to Energy Fuel Direct measurement - Bomb calorimetry Energy Changes at the Molecular Level Energy Calculated approximation using bond Calculated energies energies Bond energy – energy that must be absorbed to Bond break a given chemical bond or that is given off when a bond forms (because atoms prefer to be in bonds) in Usually given in kJ/mol Energy of a given reaction = difference between Energy energy need to break all bonds in reactants and energy released when forming all bonds in products products Energy Changes at the Molecular Level Energy Energy Changes at the Molecular Level Energy Calculating the energy of a reaction: .. .. .. → .. .. 2H − O − H .. 2H - H + O = O Energy absorbed to break all bonds in reactants 1 H-H bond x 2 moles x 436 kJ/mol = 872 kJ 1 O=O bond x 1 mole x 498 kJ/mol = 498 kJ Total = 1370 kJ Energy released by the formation of all bonds in Energy the products the 2 O-H bonds x 2 moles x (-467 kJ/mol) = -1868 kJ O-H Energy Changes at the Molecular Level Energy Calculating the energy of a reaction: .. .. .. → .. .. 2H − O − H .. 2H - H + O = O Total energy change 1370 kJ – 1868 kJ = -498 kJ 1370 Exothermic or endothermic? Negative energy change – energy is lost (given off ) – exothermic off Energy Changes at the Molecular Level Energy Energy as a Barrier Energy Activation energy (EA) – the energy needed Activation (E to initiate a reaction to Energy as a Barrier Energy High EA = very slow reaction Moderate EA = medium speed reaction Low EA = very fast reaction Fuels – want a moderate EA Speeding up slow reactions Divide fuel into small particles Increase the temperature (adding in energy) Add a catalyst – speeds up the reaction by Add providing an alternate path for the reaction that has a lower EA has Energy Consumption Energy Energy Consumption Energy Fossil Fuels Coal, petroleum, natural gas 86% of US energy energy from sunshine, stored in plants, energy preserved when dead plants are protected from oxygen from Energy Consumption Energy Coal Coal Coal Coal Advantages of Coal Very large recoverable global supply – estimated Very 20 to 40 times more coal than petroleum reserves 20 Can be used “as-is” Mining is difficult, dangerous and expensive Care is needed to avoid environmental damage at Care mining sites mining Coal is a dirty fuel – unburned soot, SOX, NOX, mercury, CO2, radioactive elements mercury, Disadvantages of Coal Disadvantages Petroleum/Gasoline Petroleum/Gasoline Advantages of oil High energy content (48kJ/g) Liquid – easier to extract from the ground and easily Liquid transported by pipeline transported Versatile – yields a variety of fuels and chemicals for other Versatile uses (plastics, pharmaceuticals, etc.) uses Petroleum/Gasoline Petroleum/Gasoline US oil consumption 5% of world’s population, 25% of world’s oil 5% consumption consumption import 57% of our oil Petroleum/Gasoline Petroleum/Gasoline What is petroleum? Mixture of thousands of different compounds Mostly hydrocarbons – molecules made up of Mostly hydrocarbons only C and H only separating petroleum into different components heat to boiling point and then condense out heat different compounds at different temperatures different Distillation Petroleum/Gasoline Petroleum/Gasoline Petroleum/Gasoline Petroleum/Gasoline In 1904 each barrel of oil gave 4.3 gallons of In gasoline and 29 gallons of kerosene gasoline Today, 19.7 gallons of gasoline, 8.4 gallons of Today, kerosene kerosene Petroleum/Gasoline Petroleum/Gasoline Making Gasoline cracking - breaking down large molecules into cracking smaller ones smaller thermal – high temperatures catalytic – use a catalyst at lower temperatures Petroleum/Gasoline Petroleum/Gasoline octane vs. isooctane Isomers – compounds with the same chemical Isomers formula, but different arrangements of the atoms (different structure) and different properties. (different Octane Isooctane BP 125°C BP 99°C BP Same heat of combustion Same Petroleum/Gasoline Petroleum/Gasoline octane vs. isooctane Octane ignites more easily than isooctane Octane will ignite when piston compresses, Octane isooctane ignites when spark plug fires isooctane Preignition of octane results in lower fuel Preignition efficiency and “knocking” efficiency Petroleum/Gasoline Petroleum/Gasoline Octane rating • Designates a gasoline mixture’s resistance to Designates knocking, relative to isooctane knocking, Petroleum/Gasoline Petroleum/Gasoline Oxygenated gasoline – blends of petroleumderived hydrocarbons with oxygencontaining compounds such as MTBE, containing ethanol or methanol ethanol Better octane ratings Petroleum/Gasoline Petroleum/Gasoline Reformulated gasoline – oxygenated gasolines that also contain less volatile hydrocarbons, such as benzene hydrocarbons, evaporate less easily than regular gasoline produce less CO reduction in VOCs – less ground level ozone 30% of US gas is reformulated, most with MTBE 30% (90%) (90%) Estimated reduction of 100,000 tons of smogforming pollutants (VOCs and NOX) and 20,000 and tons of toxics with RFG program tons MTBE is water soluble – has leaked into drinking MTBE water water So far thought to be non-toxic Petroleum/Gasoline Petroleum/Gasoline Petroleum reserves predictions: Oil extraction will soon be unable to meet demand Alternative fuels cannot make up the difference Oil production has grown in most years Ex. 67 million barrels/day globally in 2002, up 11% from Ex. 1992 1992 Since 1986 more oil is produced (extracted) than is Since discovered discovered Oil discovery has been decreasing since the 1960s One geologist predicts a peak before 2010, assuming 2 One trillion barrels still in reserves trillion U.S. Energy Information Administration predicts a peak U.S. between 2021 and 2112, assuming around 3.9 trillion barrels in reserves in Petroleum Substitutes Petroleum Synthetic fuels made from coal Blow steam over hot coke (impure carbon Blow extracted from coal) extracted C(s) + H2O(g) → CO(g) + H2(g) (water gas) Pass water gas over Fe or Co catalyst to make Pass hydrocarbons – synthetic gasoline hydrocarbons Only feasible where coal is plentiful and Only petroleum is expensive (40% of gasoline in South Africa) Africa) Petroleum Substitutes Petroleum Biomass - Materials produced by biological Biomass processes – renewable processes Ethanol Ethanol fermentation of starch and sugars in grain fermentation prepared from water and ethylene (from petroleum) energy output less than octane - 29.7 kJ/g gasohol – 10% ethanol – can be used in standard gasohol engines engines Flexible Fuel Engines can use 85% ethanol Some claim more energy goes into producing 1 gallon of Some ethanol than is gained by burning it ethanol Land use issues – 10% or the world’s energy demand Land would require 25% of the world’s cropland would Petroleum Substitutes Petroleum Biomass - Materials produced by biological Biomass processes – renewable processes Biodiesel Made from new and used vegetable oil and animal fat Made Garbage 140 power plants in US 140 1 truckload of garbage = energy of 21 barrels of oil Reduced to about 10% of original volume Biogas Animal and vegetable waste are fermented to produce biogas (methane and other gases) biogas 2/3 of rural families in China use biogas Energy Demand Energy Worldwide demand for oil increasing 2% per Worldwide year year Energy use is up in the last 10 years Energy 23% in Latin America 27% in Africa 30% in Asia China will increase oil imports from 1 million China barrels per day to 5-8 million barrels per day in the next 20 years in Projected increase of 60% in global oil Projected demand by 2020 demand Energy Demand Energy Organization for Economic Cooperation Organization estimates between 1990 and 2010 estimates Global energy consumption will rise 50% Global oil consumption will rise 40% Global coal consumption will rise 45% Global natural gas consumption will rise 66% Resulting in CO2 emissions up 50% Energy Demand Energy Conventional oil resources would last 43 at Conventional the current rate of consumption current Petroleum in heavy crude oil, bitumen and oil shale could a last another 170 years shale Global coal reserves may last a few hundred years years ~85% of petroleum is burned for fuel – rest is used for fibers, plastics, rubber, dyes, pharmaceuticals pharmaceuticals Conservation Conservation Fuel and energy use is becoming more Fuel efficient efficient Power plants are closer to maximum Power theoretical efficiencies theoretical Energy efficient appliances 18W fluorescent replacing a 75W light bulb Lasts 10,000 hours Saves electricity from 770 lbs of coal 1600 lbs less CO2 emitted 18 lbs less SO2 emitted Saves $100 in cost of generating electricity Conservation Conservation “smart” office buildings Streamlined industrial processes Example: making polyethylene (most common Example: plastic) now takes only 25% of the energy it used to to Energy to run a TV for 3 hours is saved by Energy recycling 1 aluminum can recycling Recycling Conservation Conservation Transportation 20% of total energy produced and 50% o f oil 20% production production Mid-1970s to early 1990s US gas consumption Mid-1970s dropped by 50% (lighter vehicles, better engine design) design) Since 1988 fuel economy declining Since Conservation Conservation Transportation Light duty trucks – 15% heavier and 80% more Light horsepower than 20 years ago horsepower SUVs emit 80% more CO2 than cars Trucks emit 67% more CO2 than cars Hybrid cars Methane and propane powered cars The Hydrogen Economy The Hydrogen as fuel Burn H2- instead of petroleum-based fuels or coal Less pollution – only product is water, - no CO or Less CO2 or SO2 CO High energy content – 143 kJ/g No environmental dangers from fuel spills Eliminate dependence on Middle Eastern oil Easy to produce H2 from water anywhere there is electricity electricity The Hydrogen Economy The Problem: We have no source of pure H2 It is all tied up in other molecules – a lot as water It and as hydrocarbons (fossil fuels). and Need energy from some other energy source to Need extract it extract The Hydrogen Economy The Problem: We have no source of pure H2 From water 286 kJ + H2O → H2 + ½ O2 The Hydrogen Economy The Problem: We have no source of pure H2 From fossil fuels 165 kJ + CH4 + 2H2O → 4 H2 + CO2 Thermochemical production Reactions of H2O, SO2 and I2 in high temperature nuclear reactors reactors The Hydrogen Economy The Problem: We need a way to Problem: transport and store the H2 transport takes up too much room as a takes gas has too low a boiling point to has be liquefied efficiently. be React with Li to store as LiH React solid solid Store in nanocontainers such Store as modified C60 fullerenes as ...
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This note was uploaded on 04/11/2011 for the course CHEM 102 taught by Professor Henshaw during the Winter '11 term at Grand Valley State.

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