IB Chemistry Fuels and Energy
F.1
F.1.1 Desirable characteristics of an energy source include energy being released at reasonable rates and minimal pollution.
F.1.2 Fossil fuels (very dirty), nuclear energy (still slightly infant and hard to do), electrochemical cells (too little efficientcy), wind (too little efficientcy), geothermal (too few vents that are safe).
F.2
F.2.1 Coal is formed by dead plant material that has slowly turned into mostly carbon over millions of years via exposure to high temperatures and high pressures. Oil is thought to be dead sea animal remains, and natural gas is a mixture from different sources.
F.3
F.3.1Chemical reactions rearrange atoms, nuclear reactions rearrange particles within atoms. In chemical reactions, mass is conserved and the identity of the atoms remains intact. In nuclear reactions, mass is not conserved and the atoms are transformed into different elements than the starting atoms.
F.3.2 235U → -10e + 235Np
F.3.3 alpha causes the removal of a standard helium atom, reducing atomic number and mass. Beta radiation is the release of an electron after a neutron has split into a proton and electron. Gamma radiation is a form of electromagnetic radiation and often accompanies other forms of radioactive decay.
F.3.4 Half-life is how long it take for half of a sample to decay into more stable forms. Since all radioactive decay follows first order kinetics, the half life of radioactive substances does not depend on the sample size.
F.3.5 ln(n/n0) = -kt, where n is the sample remaining, n0 is the original sample size, k is the rate of decay, and t is the time.
F.3.6 Fission is the splitting of heavy atoms. Fusion is the process of joining together light atoms to form heavy atoms. Fusion is more efficient and has easily available substances, but it has not been commercial done due to the energies required to start a stable fusion reaction. Fission is currently used in reactors to produce energy.
F.3.7 The fuel is enriched Uranium 235 or 238. The control rods are in place in order to ensure that the reaction can be controlled, as needed. The coolant allows for two different functions. This is keeping the reactor core cool as well as transfer heat to water so that the steam can be used to do work. The shielding exists in case a meltdown occurs, in which case the radioactive isotopes released will be contained.
F.3.8 Conventional power takes a lot more fuel, but is tried and true, and the fuel is easier to get. However, conventional plants causes more pollution than nuclear reactions, although nuclear reactions have waste that will not go away for millions of years.
F.3.9 Safety is a big issue in nuclear power. If the reactor temperature rises too high, a meltdown could occur. When this happens, enough heat is generated by the reactor to melt the fuel. There is not enough fissionable material present in a nuclear reactor to cause a nuclear explosion. The high temperatures present during a meltdown event can trigger chemical explosions and reactions that could release radioactive gases. However, these have been addressed with control rods and shielding, so as long as no operator errors are made, a meltdown is unlikely. Also, there was some worry over radiation, but the over 1 foot thick concrete wall around the reactor makes it impossible for even gamma radiation to pass through.
F.4
F.4.1 Solar energy can be collected from photovoltaic cells in order to make electricity; solar energy can also be used to heat.
F.4.2 Photosynthesis uses photons to create, from water and carbon dioxide, oxygen and glucose, which can then be used as fuel by the plants and by animals that eat plants.
F.4.3 Biomass con be directly converted by combustion, indirectly through the combustion of waste, production of biogas, and the production of ethanol.
F.4.4 Photovoltaic cells consist of two layers: n-type and p-type. The p-type layer acquires electrons from the n-type layer, creating a charge difference (voltage). The p-type is then hit with photons so that the electrons go back to the n-type, keeping the difference. Both types of layers are created through a process called doping. In this process, a small amount of another element is added to a crystal of silicon. For p-type, the element is a member of group 3 and creates "holes" for the electron(s). For n-type, the element is a member of group 5 and has extra electrons.
F.5
F.5.1 A Lead-acid storage battery works by using lead oxide, lead sulfate, lead plates, and sulfuric acid. An ordinary dry cell battery uses zinc, carbon, ammonium chloride, manganese dioxide and graphite dust.
F.5.2 Voltage depends on the materials used while power depends on the quantity of the materials used.
F.5.3 A hydrogen fuel cell works by oxidizing hydrogen gas and reducing oxygen gas in the prescence of a catalyst. This is strictly an electrochemical process and there is no flame produced.
F.6
F.6.1 Energy storage can be inefficient. For example, conversion to hydrogen is 60% efficient, meaning that energy that was produced was lost in an already inefficient process. However, these are the only means of capturing surplus energy for now.
F.7
F.7.1 As the neutron to proton ratio increases, beta particle decay happens. As the ratio decreases, electron capture or positron emission happens.
F.7.2 , where e is energy, ∆m is the mass defect in nuclear reactions, and c is the speed of light in a vacuum.
F.7.3 Mass defect is the amount of matter changed into energy when a nuclear reaction occurs. This is partially caused by the release of bonding energies within the nucleus.
F.8
F.8.1 Using half-life, the activity decreased by ½ after a certain amount of time.
F.8.2 Nuclear waste can come in the form of excess radiation, which can be stopped by burying the products. Also, the half-lives of the reminants is extremely long, also requiring burial.
F.8.3 See F.8.2
F.9
F.9.1 Silicon and Germanium are semiconductors
F.9.2 Metals always conduct, non-metals are insulators. Semi-conductors, since they are usually metalloids, can exhibit both properties depending on doping and creation techniques, as well as temperature.
F.9.3In p-type, silicon or germanium is doped with a group 3 atom, which has an electron hole in the trihedral connection lattice. This is then filled by passing electrons, making the effect positive. N-type comes from doping with group 5 atoms, which contain 1 too many electrons, leading to an excess that floats around, making the system negative.
F.9.4 The photons interact with the crystal structures to keep the electrons as much in the n-type region as possible, hence creating a electric potential, which causes voltage when connected to an external circuit.