CH 304K 1st EditionExam # 4 Study Guide Lectures: 30 - 38Lecture 30 (April 13)How can you calculate the change of energy of a reaction?To measure how much energy a reaction releases, you can measure the change in H using bond energies. Using a balanced reaction, Lewis structures, and a table of bond energies, you can calculate the change of H of the reaction. Change of H = sum of the bond energies of the reactants – sum of bond energies of productsLecture 31 (April 15) How can you tell if a reaction is a combustion reaction?Once you use the change of H equation to find the difference in bond energies, you can tell based on the answer. If the answer is negative, the reaction itself is losing energy which means it is giving off energy so it is a combustion reaction (an exothermic). If the number is positive, that means the reaction is endothermic. What are two methods of fracking?When breaking down crude oil to usable gasoline, depending on the composition of the crude oil it can be thermal or catalytically cracked. In order to do this you either need high temperatures (400-450 degrees C) or a lower temperature and a catalyst.Lecture 32 (April 17)What is knocking and preignition?Some gasolines burn better than others. Knocking happens when the fuel does not combust in an even shockwave away from the spark but ignites beforehand- this causes uneven temperatures and pressure inside the cylinder of the engine. Preignition is when the fuel in the combustion chamber ignites during compression before the spark plug fires.Lecture 33 (April 20)What do catalysts do?In order to start the reaction, a reactant molecule must have a minimum energy for it to react (activation energy). Reactant molecules have a range of energies. Catalysts speed up the rate of a reaction by lowering the activation energy. This means a larger proportion of reactants have sufficient energy to overcome the activation energy barrier. Also, more molecules will react in a given time which speeds up the rate of the reaction.Lecture 34 (April 22)How much power do nuclear power plant supply to the US?About 20% of the United States’ electrical power is produced by approximately 100 nuclear power stations. No new power plants were built in the US since 1978 until 2013. This is because power plants are undesirable to many people; there is a fear of the radiation and the disposal ofwaste from the plants. Explain what isotopes are.Isotopes are different versions of an element that have different number of neutrons. Different isotopes of a given element occur in different amounts. The atomic mass for any element on theperiodic table is a weighted average of all of the isotopes. To calculate it, you must not only takein to account the different isotopes, but their abundance as well.Lecture 35 (April 24)What causes radioactivity?Neutral atoms have an equal number of electrons and protons. For most smaller elements, the number of protons also equals the number of neutrons. However, for larger elements, the ratio tends to be heavier on the neutron side in order to stabilize the nucleus. When graphed, they form a “band of stability”. An atom with a neutron to proton ratio outside of the band of stability will emit radiation.Lecture 36 (April 27)What is a decay series?For some isotopes, a single type radioactive decay is often not enough to get an atom into the band of stability. If that is the case, the decay will repeat. This results in a series of steps taken by an unstable isotope to end up at one that is stable (or a decay series). The parent isotope decays to form the daughter isotope.What is fission?Fission is to crack. It is like a tiny game of pool; you shoot the cue ball at the triangle and it breaks apart. In 1938, Hahn and Strauss found that if you shot neutrons at an element, you could split a large nuclei into two smaller, lighter nuclei and a lot of energy was given off as a result. This verified Einstein’s predictions; nuclear reactions use the idea of conservation of matter/energyLecture 37 (April 29)Why do only some atoms undergo fission?Only some atoms undergo fission due to each atom’s neutron to proton ratio. Also, the speed ofthe neutrons has to be just right to fission the nucleus.Describe nuclear power.Nuclear power uses the method of fission and then uses the energy released to heat water and to then use the steam to turn the turbines. The theoretical efficiency of nuclear power is 55-60%. Nuclear plants do not emit CO2, SOx, NOx, or radioactive particles. Per pellet, the fuel possesses huge amounts of energy. The fuel pellets contain 4 g Uranium oxide and just 3-5% U-235. Plants require a coolant system with a primary, secondary, and tertiary coolant. Control rods contain substances (cadmium, silver, indium) that absorb neutrons. Moderators are substances that slow down neutrons so they are more likely to induce fission. Control rods and moderators are extremely important because if there aren’t enough or too many neutrons, the nuclear reactor “goes critical” (which is bad).Lecture 38 (May 1)What does radioactivity do to the human body?Alpha, beta, gamma, X, and cosmic rays are all ionizing radiation. They form radicals that can react with the DNA inside cells and cause them to die or mutate with can cause cancer. Rapidly dividing cells are the most vulnerable to radiation (stomach cells, skin cells,