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Mizzou CHEM 1100 - Exam 4 Study Guide

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Chem 1100Exam # 4 Study Guide Lectures: 17 - 20Lecture 17 (November 3rd)Energy/ElectricityPower Plants: Burn coal  heat water  turn turbine  electricityBattery: Stored energy, converts chemical to electricalGalvanic Cells: Chemical  electricalElectrolytic Cell: Electrical  chemicalElectricityThe flow of electrons.Chemistry: making and breaking chemical bonds.Bonds = electronsChemical reactions: some involve sharing electrons and others involve transferring electrons to produce electricity.Oxidation Reaction: include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between species.Half Reactions: 2 Na + Cl2  2NaClShows electron transfer: 2Na  2Na+ + 2e- Na loses e- (oxidation)Cl2 + 2e-  2Cl- Cl gains e- (reduction)BatteriesOxidation Is Loss Reduction Is GainNickel-Cadmium Battery: a storage battery with a negative electrode made of cadmium, a positive electrode of nickel oxide, and a solution of potassium hydroxide as the electrolyte. Nickel-cadmium batteries have the advantage of an airtight battery container, which prevents the corrosive electrolyte from leaking.How to Make Electricity: Separate the half reactions  connect with a wire  only way for the reaction to go is for the electron to run through the wire  The electron flow = the electric current.ElectrodesElectrical conductors – sites of the reactionsCathode: reduction occurs – electrons gainedAnode: oxidation occurs – electrons lostVoltageEase of anode electron releaseEase of cathode electron absorptionUnits are called VoltsSalt Bridge: Allow ions to transfer through them. It’s made of ionic compounds that allow ions to travel.What do we want from our batteries?  High voltage (energy efficient), cheap, long lasting, safe handling and disposal, small, & lightStorage Battery: We use them in our cars. They have 6 cells inside them with each capable of putting out 2 volts of energy. Stores electrical energy. Ex: Lead-acid. Six 2.0 V cells  12.0 VWhy not use batteries to power everything?  Efficiency  Power plants: 30-40%  Batteries: 90% It would be very expensive to power everything with batteries because batteries are expensive to make and also people don’t always dispose of them appropriately. Rechargeable batteries don’t last forever so disposal is still an issue.Where does the power come to recharge batteries? Power plant.Alternative to batteries  Fuel Cells  Chemical energy is turned into electrical energy  No fire/explosion  Fuel and oxidant supplied, “waste” expelled continuously  Half reactions separate.Lecture 18 (November 5th) Fuel Cells: Force hydrogen atoms through membranes  Carbon atoms through wire No flame, no solids needed  all gas  Little heat (efficient)  good thing bc we aren’t losing as much energy Produces = H2O (environment friendly) Unused Hydrogen and Oxygen can be put back in the fuel cell  It’s 40-45% efficient which compares to gas engines (20-30%) and diesel (30-35%)Fuel Cell in Cars: No nitrogen oxides  Low to no C02 emissions  Hydrogen and methanol could be renewable resources? They are doing research on it now.Engine: no moving parts in engine. The fewer moving parts you have the less you have to repair and the easier it is to repair. It’s longer lasting. AdvantagesWill run as long as your fuel/hydrogen/methanol tank, It’s a lot faster than it takes to recharge an electric cars battery, The reaction is slower and there’s not as much power in a short time, Upfront costs for these fuels cells are expensive but cheaper in the long run.Sources of HydrogenHydrogen is the most plentiful element (93%), Very reactive  tied up in compounds, It must be extracted.Where do we get the energy to extract it?Not from power plants: they are only 20-30% efficient (50% at best), Heat decomposition? Takes too much energy Need 5000 degrees C, Catalysis: Water gas reaction, Theobjective is to make the catalyst react at low temperatures, Making ammonia and transporting in that form but they are afraid drug dealers would steal the ammonia to make meth, Storage inNanotubes: tubes of carbon atoms, They are heavy and explosive and have to be transported in pressurized cylindersElectric CarsLead storage batteries, No pollutants released, Don’t need fuel, NiMH and Li-Ion, Light  better mileage, Last life of vehicle, Quick recharge, Needs frequent recharge  short range, Recharge Stations would be needed in many places, Need power plants to fuel these recharge stations, Power plants = pollutants, Toxic materials (point source) – limited rechargesLecture 19 (November 10th) Hybrid CarHas 2 engines, Gas engine & NiMH/Li-Ion – battery never drained completely, Car runs off the battery and as soon as it reaches a certain level the car starts running off of the gasoline engine and simultaneously recharges the battery. Environmentally Friendly, Big upfront cost, the performance must match that of conventional vehicles or there wouldPhotovoltaicElectrical potential based on light. Take energy from the sun. The sun is renewable energy. Light/heat is not very useful for work. Low order type energy. If we can collect enough in a small enough space it can generate electricity. It’s used today in hydrogen production. Use energy for the sun and hook it up to a solar cell and use it to make hydrogen gas.Semiconductors: Only conducts under specific conditions, Photon of right wavelengths collide, Silicon (4A) – the photon of 1100 nm will knock electrons off, Problems – they cost a lot of energy to make and you have to refine it to a very high purity, which is very expensive. Also theyhave low efficiency. The max is 28% and reality is more like 10-17% but the energy is free and unlimitedDevelopmentsNon-crystalline silicon – decreases cost and increases efficiency. Doping silicon – combined with other materials like Arsenic and Gallium. As (5A) one more outer electron. Ga (3A) one less outer electron.Doped SiliconArsenic: has the extra electron and we call that n-type (negative). The arsenic is not really charged we just call it that. Gallium is electron deficient and we call that p type (positive). Gallium is not really charged we just call it that. Easier to make an electron current and get them going. We have different layers of n and p type and the electrons flow between them.Solar ThermalA trough with


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