Mizzou CHEM 1100 - Exam 4 Study Guide (5 pages)

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Exam 4 Study Guide

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Exam 4 Study Guide


Study Guide Exam 4

Study Guide
University of Missouri
Chem 1100 - Atoms and Molecules With Lab
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Chem 1100 Exam 4 Study Guide Lectures 17 20 Lecture 17 November 3rd Energy Electricity Power Plants Burn coal heat water turn turbine electricity Battery Stored energy converts chemical to electrical Galvanic Cells Chemical electrical Electrolytic Cell Electrical chemical Electricity The flow of electrons Chemistry making and breaking chemical bonds Bonds electrons Chemical 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 2NaCl Shows electron transfer 2Na 2Na 2e Na loses e oxidation Cl2 2e 2ClCl gains e reduction Batteries Oxidation Is Loss Reduction Is Gain Nickel 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 Electrodes Electrical conductors sites of the reactions Cathode reduction occurs electrons gained Anode oxidation occurs electrons lost Voltage Ease of anode electron release Ease of cathode electron absorption Units are called Volts Salt 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 light Storage 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 V Why 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 Advantages Will 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 Hydrogen Hydrogen 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 The objective 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 in Nanotubes tubes of carbon atoms They are heavy and explosive and have to be transported in pressurized cylinders Electric Cars Lead 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 recharges Lecture 19 November 10th Hybrid Car Has 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 would Photovoltaic Electrical 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 they have low efficiency The max is 28 and reality is more like 10 17 but the energy is free and unlimited Developments Non 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 Silicon Arsenic 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 Thermal A trough with mirrors that reflect light on a central pipe that has liquid in it and the sun heats up the liquid and they pump that liquid to generate electricity Wind farms are a significant upfront investment but worth it Geothermal energy drill holes deep into the earth close to the core and draw heat from there You can t do this anywhere It s

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