Chem ch24

Worked solutions to student book questions Chapter 24 Alternative energy sources

Heinemann Chemistry 2 4th edition Enhanced Copyright Pearson Australia 2010 (a division of Pearson Australia Group Pty Ltd) 1

E1. Australia and China are both signatories to the Treaty for the Non Proliferation of Nuclear Weapons. Use the Internet to find out about the purposes of this treaty.

AE1. The treaty has three goals.

To stop the spread of nuclear weapons Nuclear disarmament Support the peaceful use of nuclear technology

E2. Identify some of the issues involved in the mining of uranium and its sale to other countries.

AE2. Environmental issues associated with mining, e.g. water and soil contamination. Right of traditional landowners. Health issues related to exposure to radioactive materials. Use of uranium to make weapons. Disposal of spent fuel.

Q1. Australia exports most of the uranium it mines rather than using it for domestic nuclear power stations. Respond to each of the following questions, giving the reasons for your response in point form. a Should Australia take back the waste products from nuclear power stations

fuelled by Australian uranium? b What possible changes might lead to a greater use of nuclear power in Australia?

A1. a Issues to consider include whether the user or supplier should be responsible for

the waste, and whether radioactive wastes should be stored in the most cost-effective and environmentally safe place, regardless of where the uranium comes from.

b Factors that might lead to increased use of nuclear power in Australia include improved waste-storage techniques and decreased availability or increased cost of other energy sources.

Q2.

Bagasse, the fibrous waste from sugarcane mills, is burnt to satisfy about 2 per cent of Australias energy needs. Firewood satisfies a similar amount. Should we use more or less of these renewable resources? Justify your answer.

A2. In order to conserve non-renewable resources, the use of renewable resources should be encouraged but only so far as it can be sustained in the foreseeable future. Beyond this limit, even renewable resources will eventually be exhausted because the rate of supply (e.g. growth of forests) will not match the rate of use (e.g. removal of trees). As non-renewable resources diminish and become more expensive, the use of renewable resources, such as bagasse, will become more economically attractive.



Q3. a Select a form of biochemical energy and one other form of renewable energy. For

your chosen energy sources: i draw up a table that summarises their advantages and disadvantages ii comment on their usefulness in supplying the future energy needs of your

local community. b Repeat part a for two non-renewable forms of energy.

A3. a i Renewable energy sources include wind, tidal, hydro-electric, wave, biomass

(e.g. wood) and solar power. Advantages include the fact that these are sustainable energy supplies, and have low environmental impact in some cases (e.g. wind power).

Disadvantages include variable rate of supply (e.g. solar energy), rate of supply generally insufficient to meet the current needs of society, current technological limitations on the collection and storage of energy.

ii It is expected that renewable energy sources will become more useful in future as supplies of non-renewable energy sources diminish.

b i The advantages of many non-renewable energy sources include their high and controllable rate of supply at present, their relatively low cost, and the fact that the technology exists to use these energy sources.

Disadvantages include finite quantity and future exhaustion, expected future cost increases, significant environmental impact in some cases (e.g. nuclear accident, acid rain).

ii It is expected that non-renewable energy sources will remain useful in future in so far as diminishing supplies will permit. It is hoped, but by no means guaranteed, that improved technology will allow us to better harness renewable resources and so to reduce the communitys dependence upon non-renewable resources.

Chapter review

Q4. a Write an overall equation for the formation of plutonium-239 from a neutron

hitting uranium-238 in a nuclear reactor. Hint: Use electrons (beta particles, 01 ) in your equation.

b Plutonium can be used to make atomic weapons. What implications does this have for global security when a nation decides to introduce nuclear power? Suggest some safeguards to minimise nuclear proliferation.

A4.

a 1 238 239 00 92 94 1n + U Pu + 2 b The capacity for nuclear power generation increases the possibility of a nation

developing nuclear weapons. Safeguards include prohibition of nuclear power development, monitoring nuclear programs, international agreements/treaties and economic and/or military intervention against rogue nations and/or terrorists (issues remain about who the global police should be).



Q5. Research the characteristics of some radioactive isotopes in spent nuclear fuel that make them particularly hazardous to human health.

A5. Hazardous properties include the emission of radiation (particularly alpha particles and gamma rays that can directly damage tissues and mutate DNA), long half-lives and chemical properties that allow dispersal including movement through the food chain.

Q6. Australia has large reserves of uranium. At present, it has no nuclear power stations and exports only a limited amount of this source of energy. Discuss with other members of your class the benefits and costs associated with the following proposals: a that Australia should build nuclear power stations b that mining of uranium should be banned

A6. a Benefits of building nuclear power stations in Australia include reduced

dependence upon energy supplies from overseas; increased employment opportunities; reduced use of other energy resources; reduction in the pollution associated with fossil-fuelled power production. Costs include environmental impact of uranium mining; disposal of nuclear wastes; health and environmental hazards associated with nuclear accidents; risk of terrorist activity motivated by the need to obtain nuclear materials; increased risk of Australia being a target in a nuclear war.

b Benefits of mining uranium include local employment, export revenue, benefits of nuclear power stations (see part a). Costs include environmental impact of mines; possible use of uranium for military purposes; disadvantages of nuclear power stations (see part a).

Q7. The coal versus nuclear power debate has undergone a recent revival in Australia. a Given the choice, would you prefer to live near a coal-fired power station or a

nuclear power station? Why? b Is there just a choice between coal and nuclear power as they now operate? What

other options exist?

A7. a Considerations include type of pollution and extent to which it occurs, health and

environmental risks of pollutants, and chances of a major catastrophe and its likely consequences. The immediate environment around a nuclear power station is usually cleaner and healthier than that around a coal-fired power station, but a nuclear accident may cause fatalities and have other long-term consequences.

b Other options include alternative energy sources and improved technology to deal with hazards and sustainability issues related to coal and nuclear fuels. Research and development is expected to be critical in improving societys choice of energy sources.



Q8. Oil, coal and natural gas are described as non-renewable sources of energy. List three examples of renewable sources of energy.

A8. Examples include ethanol (from crops), and solar, tidal, wave and wind power.

Q9. The use of solar energy in Australia is increasing. About 6% of dwellings have solar water-heaters, and around 30 000 new solar water-heaters are being produced each year. a What situations are most suited to the use of solar water-heaters? b Why do you think that the use of solar water-heaters is not more widespread? c Solar cars can be constructed and they are cheap to run. Why then do most people

prefer petrol-driven cars?

A9. a Compared with heaters that run on oil, gas or electricity, solar water heaters have

only been introduced relatively recently and the technology involved is still being developed. These heaters are likely to become increasingly popular as they become more efficient and as older heaters wear out or become too expensive to operate. Solar water heating is feasible in all parts of Australia but is more likely to be used in isolated places where other energy supplies are difficult to obtain. It is particularly useful in situations where the hot water is used on-site and where low running costs are important.

b Existing technologies tend to be only slowly replaced with new developments unless the latter offers dramatic economic benefits. At present, solar water heaters are marketed mainly in the sunnier northern regions of Australia. However, in the future it is likely that the use of these heaters in all regions will become more widespread.

c Current models of the solar car cannot store as much energy as petrol-driven cars of similar mass. Despite being cheaper, cleaner and quieter, solar cars tend to be slower and smaller and are dependent on the weather.



Q10. Every day each one of us uses energy supplied by our society. a Summarise the energy that you are supplied with from outside sources in a single

day. Identify the energy source (e.g. coal, gas, etc.) and its application (e.g. transport, hot water, etc.) in your answer.

b How could you change your days activities so that your energy use is minimised? Can you make a difference?

A10. a For example:

Source Application electricity electricity gas oil

hair dryer toast and tea shower car or bus

b Low-energy alternatives for the applications above are: air-dry hair, have a cold

breakfast, short shower and walk or cycle. If each of us conserves energy, we can make a difference.

Q11. The ever-increasing use of computer-controlled systems offers opportunities for increasing our societys efficiency in using energy. Describe how energy can be saved by the computer control of: a engines in cars b traffic systems c household lights and heating d industrial production systems.

A11. a Improved engine tune wastes less petrol. b Reduced travel times waste less petrol. c Energy for heat and light is required for shorter periods. d Continuous monitoring of raw materials and products can provide feedback to

maintain optimum energy consumption for industrial processes.

Q12. Changes in energy consumption over time are shown in Figure 23.3 (p. 368). a In which decade was nuclear energy introduced? What events led to the

introduction of this form of energy? b Why has wood not shown the same increase in consumption as other fuels? c Suggest why the rate of use of coal was outstripped by the rate of use of oil. d Describe four ways in which the use of energy in the daily life of a person living

in an Australian city in 1860 would have differed from that of a person living now.



A12. a The world community was introduced to the devastating power of nuclear energy

when an atomic bomb was exploded in 1945, during World War II. Several years later the research that led to the development of the atomic bomb was applied to the peaceful purpose of electrical power generation.

b The use of other fuels such as coal, oil and uranium has increased at a faster rate than the use of wood because the former have been more suitable for a range of applications due to their lower cost, high energy content per unit mass, ease of transport and distribution, or more controllable combustion. The limited availability of wood greatly restricts its use as a fuel.

c Oil is a more versatile fuel than coal. The various fractions available from crude oil enable a range of fuels for specialised uses to be producedfor example, high-octane petrol for racing cars and diesel for trucks. Oil also has a higher energy content per unit mass than coal, is more conveniently handled and produces fewer pollutants when burnt.

d We now use much more energy for transport, production of consumer goods and for heating. Coal, wood and animals were the major sources of energy in the 1860s, with relatively little use of oil and gas. While coal is still a major fuel today, the use of nuclear, solar, wave, tidal and wind power has become more extensive. Our current consumption of oil and the widespread delivery of energy in the form of electricity distinguish the 1990s from the 1860s.

Q13. Tasmania obtains nearly all of its power supplies from hydroelectricity, whereas Victoria obtains over three-quarters of its electricity from brown coal. Account for the difference between the two states in methods of energy production.

A13. Both Tasmania and Victoria have chosen to use the most readily available natural resources for their energy supplies. Tasmanias high rainfall and small population mean that hydro-electricity is able to supply most of its energy needs. The abundance of brown coal in Victoria has made coal a more suitable source of energy for that state.

Q14. Most forms of energy available to us originated from energy supplied by the Sun. a Justify this statement by explaining the origins of wind energy, oil and

hydroelectricity. b List the energy transformations involved in generating electricity from biogas.



A14. a Wind is the result of the uneven heating of the planet by solar radiation. The

tropics receive more solar radiation per square metre than the poles. Air in the warmer locations expands and becomes less dense. The warm air rises and winds are created as neighbouring air moves into the low-pressure region that is created. The energy in oil was originally present in the plants and animals from which the oil was made. The plants obtained energy from the sun directly via photosynthesis and the animals obtained energy indirectly, via a food chain which began with plants. The gravitational potential energy of water in a dam is due to the evaporation of water from a low altitude to a higher altitude; the evaporation is a consequence of solar energy.

b chemical energy in waste chemical energy in biogas thermal energy from combustion of biogas thermal energy of steam mechanical energy of turbine electrical energy of generator

Q15. The Yallourn power station in Victoria has a maximum capacity of 1450 MW. The average daily rate at which Melbourne receives solar energy is 1.0 kW m2. a What area of solar cells, operating at 20% efficiency, would produce the same

amount of power as the Yallourn station? b If a typical residential block of land in the city has an area of 750 m2, how many

of these blocks does your answer in part a represent?

A15. a Step 1 Calculate the energy produced by solar cells. Solar energy per cell = 1.0 kW m2 10% = 0.10 kW m2 Step 2 Calculate the area of solar cells required.

Area of solar cells = metre squareper energy

requiredenergy total

= 23

mkW 0.10kW 101450

= 1.450 107 m2 = 1.5 107 m2 (two significant figures)

b Number of blocks = areablock city area cellsolar

= 227

m750m 101.45

= 1.9333 104 blocks = 1.9 104 blocks (two significant figures)



Q16. Is there an energy source that may be used without any environmental impact? Explain your answer.

A16. The use of any energy source will have a degree of environmental impact. The important consideration when choosing and using an energy source is the extent and nature of the impact. It is a matter of weighing the degree to which an energy source benefits the community against its environmental cost.

Q17. Describe how you expect energy to be provided in the year 2050 for each of the following purposes. Give reasons for your answers. a domestic hot water b domestic lighting c private transport d industrial heating

A17. Include reference to the expected availability of the energy source in the year 2050 (e.g. less oil and gas); consider the environmental impact of energy uses (e.g. acid rain from burning coal), the need to conserve energy, and the development of new technology for using energy.

Q18. Compare the diagrams showing the operation of a coal-fired power station (Figure 23.10 on page 372 of the student book), nuclear power station (Figure 24.3 on page 384 of the student book) and hydroelectric power station (Figure 24.34 on page 391 of the student book). a In what ways are the power stations similar? b How do they differ? c Name an advantage and a disadvantage of each form of energy production.

A18.

a The power stations all convert mechanical energy in a turbine into electrical energy. Nuclear and coal-fired power stations both use hot steam to turn their turbines, whereas running water is used in a hydro-electric power station.

b Nuclear power stations convert nuclear energy into thermal energy, which then becomes thermal energy of steam; coal-fired power stations convert chemical energy to thermal energy of steam; hydro-electric power stations convert the gravitational potential energy of water in a dam to the kinetic energy of falling water. The power stations also differ in the type and extent of their environmental impact. Only the hydro-electric power station uses a renewable energy source.



c For coal-fired power stations: Advantages include large Australian coal reserves, low cost. Disadvantages include pollution to the local environment, non-renewable.

For nuclear power stations: Advantages include large Australian uranium reserves, high energy output per mass of fuel, low accident rate, reduced fossil fuel consumption, little pollution near the power stations. Disadvantages include disposal of radioactive waste, devastating impact of accidents, non-renewable.

For hydro-electric power stations: Advantages include renewable, little pollution, low running costs. Disadvantages include restricted sites, fact that dam destroys local habitat.

Q19. Coal, oil, nuclear energy and solar energy are all important sources of energy today. Give your opinion of the likely importance of each source of energy in: a 10 years time b 100 years time c 1000 years time

A19. a Trends in energy use would seem to indicate an increase in our reliance on

renewable sources such as solar energy, with a slow movement away from oil to coal and natural gas as Australias reserves begin to decline.

b In 100 years time, if current rates of consumption persist, it is likely that oil reserves will have run out, although coal reserves may still supply a considerable proportion of the worlds energy. Opinions are divided about the likely importance of nuclear energy and renewable forms of energy such as solar energy. Research into nuclear fusion may have developed sufficiently for it to have become a major source of energy.

c Naturally, what human beings will be using as sources of energy in 1000 years time is even more uncertain. Fossil fuel reserves are likely to have become a minor source of energy.

Chem ch24

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