energy_sources

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Section Preview/ Specific Expectations In this section, you will m compare the efficiency and environmental impact of conventional and alternative sources of energy m communicate your under- standing of the following terms: non-renewable, renewable The energy that Canadians use comes from a variety of sources. What factors account for the changes you can see in this graph? How do you think energy use has changed since 19967 Energy Sources Canadians depend on energy sources, such as those listed in Figure 5.18, to power vehicles, light and heat buildings, and manufacture products that support our lives and lifestyles. As society’s needs for energy and energy-using products grow, scientists and technologists search for more economical and environmentally responsible ways to meet these needs. In this section, you will compare energy sources based on their efficiency and environmental impact. Primary Energy by Source, Canada, 1871 to 1996 (Percent of Energy Consumption) Percent 0 - T T 1871 1895 1915 1935 1955 1975 T T T 1 1996 = Wood Coal = Petroleum - Hydro Gas Nuclear Energy and Efficiency When you think about energy efficiency, what comes to mind? You may think about taking the stairs instead of the elevator, choosing to drive a small car instead of a sport utility vehicle, or turning off lights when you are not using them. What, however, does efficiency really mean? How do you quantify it? There are several ways to define efficiency. One general definition says that energy efficiency is the ability to produce a desired effect with minimum energy expenditure. For example, suppose that you want to bake a potato. You can use a microwave oven or a conventional oven. Both options achieve the same effect (baking the potato), but the first option uses less energy. According to the general definition above, using the microwave oven is more energy-efficient than using the conventional oven. The general definition is useful, but it is not quantitative. Another definition of efficiency suggests that it is the ratio of useful energy produced to energy used in its production, expressed as a percent. This definition quantitatively compares input and output of energy. When you use it, however, you need to be clear about what you mean by “energy used.” Figure 5.19 shows factors to consider when calculating efficiency or analyzing efficiency data. 256 MHR - Unit 3 Energy Changes and Rates of Reaction
"Useful energy” is m energy delivered to consumer in usable form = actual work done 1 Useful energy produced Efficiency = X 100% Energy used "Energy used” could include = ideal energy content of fuel T = energy used to extract and transport fuel m solar energy used to create fuel (e.g. biomass) = energy used to build and maintain power plant GIMZXAL) Efficiency is expressed as a percent. Always It is often difficult to determine how much energy is used to produce specify what is included in the useful energy. Often an efficiency percent only takes into account the “energy used” part of the ratio. “ideal” energy output of a system, based on the energy content of the fuel. Efficiency and Natural Gas When discussing the efficiency of a fuel such as natural gas, you need to specify how that fuel is being used. Consider, for example, natural gas. Natural gas is primarily methane. Therefore, you can estimate an ideal value for energy production using the enthalpy of combustion of methane. CHy(g) + 203() > COgg + 2H;0ry) AH" =-802 k] In other words, 16 g of methane produces 802 k] of heat (under constant pressure conditions). When natural gas is used directly in cooking devices, its efficiency can be as high as 90%. Thus, for every 16 g of gas burned, you get about 720 k] (0.90 x 802 kJ) of usable energy as heat for cooking. This is a much higher fuel efficiency than you can get with appliances that use electrical energy produced in a power plant that runs on a fuel such as coal. If natural gas is used to produce electricity in a power plant, however, the efficiency is much lower—around 37%. Why? The heat from the burning natural gas is used to boil water. The kinetic energy of the result- ing steam is transformed to mechanical energy for turning a turbine. The turbine generates the electrical energy. Each of these steps has an associated efficiency that is less than 100%. Thus, at each step, the overall efficiency of the fuel decreases. Thinking About the Environment Efficiency is not the only criterion for selecting an energy source. Since the 1970s, society has become increasingly conscious of the impact of energy technologies on the environment. Suppose that you want to analyze the environmental impact of an energy source. You can ask the following questions: e Are any waste products or by-products of the energy production process harmful to the environment? For example, any process in which a hydrocarbon is burned produces carbon dioxide. Carbon dioxide is a known greenhouse gas, which contributes to global warming. Any com- bustion process provides the heat required to form oxides of nitrogen from nitrogen gas. Nitrogen oxides contribute to acid precipitation. e Is obtaining or harnessing the fuel harmful to the environment? For example, oil wells and strip coal mines destroy habitat. Natural gas GTMTXET] This gas pipeline pipelines, shown in Figure 5.20, are visually unappealing. They also harms the ecosystem by splitting split up habitat, which harms the ecosystem. up habitat. Chapter 5 Energy and Change « MHR 257
e Will using the energy source permanently remove the fuel from the environment? A non-renewable energy source (such as coal, oil, or natural gas) is effectively gone once we have used it up. Non-renewable energy sources take millions of years to form. We use them up at a much faster rate than they can be replenished. An energy source that is clearly renewable is solar energy. The Sun will continue to radiate energy toward Earth over its lifetime—many millions of years. A some- what renewable energy source is wood. Trees can be grown to replace those cut down. It takes trees a long time to grow, however, and habitat is often destroyed in the meantime. Comparing Energy Sources Both efficiency and environmental impact are important factors to con- sider when comparing energy sources. In the following ThoughtLab, you will research and compare alternative and conventional energy sources. Comparing Energy Sources In this ThoughtLab, you will work as a class to fuels back to solar energy that powered the . compare two different energy sources. photosynthesis in the plants that eventually became the fossil fuel. Write a brief outline of Procedure your findings. 1. On your own, or with a group, choose an energy 6. Your teacher will pair you (or your group) with source from the following list. Other energy another student (or group) that has researched a sources may be discussed and added in class. different energy source. Work together to analyze solar (radiant) energy wood the comparative merits and drawbacks of the two petroleum biomass energy sources, based on your research. hydrogen fuel cell LI EEY R0 1. Write a conclusion that summarizes the benefits nz?tural gas fuel cell natural gas and risks of both energy sources, in terms of Lol EEETY Bkl their efficiency and environmental impact. hydroelectric power tar sands geothermal energy 8. Present your findings to the class. 2. Before beginning your research, record your cur- Analysis rent ideas about the efficiency and environmental ) 1. Discuss the presentations as a class. impact of your chosen energy source. (a) Decide which energy sources are most 3. Research the efficiency and environmental efficient. Also decide which energy sources impact of your energy source. If possible, are least damaging to the environment. determine what the efficiency data means. For example, suppose that a source tells you that natural gas is 90% efficient. Is the source referring to natural gas burned directly for heat or for cooking? Is the energy being converted from heat to electricity in a power plant? Be as specific as possible. (b) Decide which energy source is best overall in terms of both efficiency and environmental impact. 2. Could the “best overall” energy source be used to provide a significant portion of Canada’s energy needs? What obstacles would need to be overcome for this to happen? 4, Ensure that you use a variety of sources to find your data. Be aware of any bias that might be present in your sources. 3. Besides efficiency and environmental impact, what other factors are involved in developing and delivering an energy source to consumers? 5. Trace the energy source as far back as you can. For example, you can trace the energy in fossil | | e SE——— e e | 258 MHR - Unit 3 Energy Changes and Rates of Reaction
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Nuclear Safety Supervisor CE = = _ Jennifer Noronha In some ways, nuclear power is an appealing power source. Nuclear reactions create large amounts of energy from minimal material, and they generate none of the carbon dioxide and other emissions that cause acid rain and global warming. The products and reactants of nuclear reactions, however, are dangerously radioactive. Therefore, special meas- ures are needed to protect nuclear power station employees from daily exposure to radiation. That is where Jennifer Noronha comes in. Noronha is the supervisor of Radiological Services at Darlington. Employee safety—especially from high radiation doses—is her first priority. The Darlington Nuclear Generating Station is located 70 km east of Toronto. It uses a fuel of natural uranium to produce enough electricity to provide power for a city the size of Toronto. Noronha and her radiation protection team plan and implement safety programs that minimize dose rates, or the amount of radiation that station employees are exposed to. Station employees must undergo four weeks of radiation protection training. This training was designed by Noronha’s department, based on an extensive investigation of radiation fields within the station, as well as a thorough evaluation of past safety programs and approaches. Through this training, employees learn how to measure existing dose rates with survey equipment, assess what kinds of tools and protective clothing are needed, and take appropriate action to lower radiation doses. For example: e Airborne hazards, such as tritium (present in radiated water vapour), can be reduced by running the station’s dryer system. The dryer system catches the radiated vapour and dries it out of the air. e Non-airborne radiation can be countered by shielding the affected area with lead blankets or sheeting material. Noronha’s strong mathematics skills were evident from an early age. When she moved to Canada from Kenya at age 11, she was immediately put ahead a grade. Her mathematics skills and her father’s engi- neering profession were what propelled her toward engineering. Noronha earned her engineering physics degree from McMaster University. Her courses included general chemistry, biomedical theory, and nuclear theory. She worked as a commissioning engineer at Darlington during its start-up. She tested the station’s safety shut-down systems and helped to bring the station’s first reactor on-line. “It was pretty amazing,” Noronha says. “At the time, it was still relatively new technology, and it was Canadian technology.” Noronha got her MBA from the University of Toronto in 1998. Soon after, she moved to her current position, which allows her to combine her people skills and technical expertise. Making Career Connections 1. Are you interested in the different safety con- cerns related to Canadian nuclear reactors, and the steps that are being taken to counter these concerns? Contact the Canadian Nuclear Safety Commission (CNSC) or explore their web site. (The CNSC is the Ottawa-based government watchdog for the use of nuclear energy in Canada.) 2. To learn more about the wide variety of careers in nuclear power generation, Ontario Power Generation is a good place to start. Their web site has a helpful career page that lists opportuni- ties for students and recent graduates, as well as experienced professionals. Chapter 5 Energy and Change * MHR 259
Chemistry Bulletin EIET) XN EEEET) Hot Ice When engineers first began extending natural gas pipelines through regions of bitter cold, they noticed that their lines plugged with a dangerous slush of ice and gas. The intense pressure of the lines, combined with the cold, led to the formation of methane hydrates, a kind of gas-permeated ice. More than a mere nuisance, methane hydrate plugs were a potential threat to pipelines. The build-up of gas pressure behind a methane hydrate plug could lead to an explosion. Now, however, this same substance may hold the key to a vast fuel supply. Methane hydrates form when methane molecules become trapped within an ice lattice as water freezes. They can form in very cold conditions or under high-pressure conditions. Both of these conditions are met in deep oceans and in permafrost. In Canada, hydrates have already been found in large quantities in the Canadian Arctic. Methane hydrate has a number of remarkable properties. For example, when brought into an oxygen atmosphere, the methane fumes can be ignited, making it appear that the ice is burning! Methane releases 25% less carbon dioxide per gram than coal, and it emits none of the oxides of nitrogen and sulfur that contribute to acid precipitation. Therefore, using methane in place of other fossil fuels is very desirable. Methane hydrates seem to be an ideal and plentiful “pre-packaged” source of natural gas. Estimates of the exact amount of methane stored in hydrates suggest there could be 260 MHR - Unit 3 Energy Changes and Rates of Reaction l':mrfrr.nmr:r:.’J enough to serve our energy needs anywhere from 350 years to 3500 years, based on current levels of energy consumption. This would con- stitute a significant source of fossil fuels, if we can find a way to extract the gas safely and economically. Unfortunately, hydrates become unstable when the pressure or temperature changes. Even small changes in these conditions can cause hydrates to degrade rapidly. Methane hydrates are stable at ocean depths greater than 300 m, but offshore drilling at these depths has been known to disturb the hydrate formations, causing large, uncontrolled releases of flamma- ble methane gas. Also, methane hydrates often hold sediment layers together. Therefore, in addition to the danger of a gas explosion, there is the danger of the sea floor collapsing where drilling occurs. Methane is a significant greenhouse gas. A massive release of methane could cause catastrophic global climate change. Some researchers believe that the drastic climate change that occurred during the Pleistocene era was due to methane hydrate destabilization and widespread methane release. Nonetheless, Canada, Japan, the United States, and Russia all have active research and exploration programs in this area. As global oil supplies dwindle, using methane hydrates might increasingly be seen as worth the risk and cost. Making Connections 1. Compare using methane from natural gas with using methane from methane hydrates in terms of environmental impact and effi- ciency. You will need to do some research to find out extraction methods for each source of methane. 2. On the Internet, research one possible struc- ture of methane hydrate. Create a physical model or a three-dimensional computer model to represent it. Use your model to explain why methane hydrates are unstable at temperatures that are warmer than 0°C.
Emerging Energy Sources In the Thoughtl.ab on page 258, you probably noticed that all energy sources have drawbacks as well as benefits. Scientists and engineers are striving to find and develop new and better energy sources. One energy source that engineers are trying to harness is nuclear fusion. As you learned in section 5.1, nuclear fusion provides a great deal of energy from readily available fuel (isotopes of hydrogen). In addition, nuclear fusion produces a more benign waste product than nuclear fission (helium). Unfortunately, fusion is not yet practical and controllable on a large scale because of the enormous temperatures involved. Chemists are also striving to find new sources for existing fuels that work well. The Chemistry Bulletin on the facing page discusses a new potential source of methane. Section Summary In this section, you learned about efficiency. You learned how it can be defined in different ways for different purposes. You used your understanding of processes that produce energy to investigate the efficiency and environmental impact of different energy sources. In Chapter 5, you learned about the energy that is associated with chemical reactions. You used a calorimeter to measure heat changes, and you used these heat changes to write thermochemical equations. You probably already realize that adding heat to reactants often speeds up a reaction. In other words, raising the temperature of a system consisting of a chemical reaction often increases the speed of the reaction. A familiar example is cooking. You increase the temperature of a heating element to speed up the reactions that are taking place in the food as it cooks. How does increasing temperature speed up a reaction? Is the enthalpy of a reaction related to its speed? Chapter 6 addresses these questions. Section Review © O Your friend tells you about an energy source that is supposed to be 46% efficient. What questions do you need to ask your friend in order to clarify this claim? © O Efficiency and environmental concerns are not always separate. In fact, they are often closely linked. Give three examples of energy sources in which changes in efficiency affect environmental impact, or vice versa. © O Design an experiment to determine the efficiency of a laboratory burner. You will first need to decide how to define the efficiency, and you will also need to find out what fuel your burner uses. Include a complete procedure and safety precautions. © D Some high-efficiency gas furnaces can heat with an efficiency of up to 97%. These gas furnaces work by allowing the water vapour pro- duced during combustion to condense. Condensation is an exothermic reaction that releases further energy for heating. Use the information in this section to demonstrate the increased heat output, using Hess’s law. The enthalpy of condensation of water is 44 kJ/mol. Chapter 5 Energy and Change - MHR 261
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