Chapter 10: Energy
- The simplest definition of energy is that it is the capacity to do work.
- Work may be defined as what is done to move an object against some sort of resistance.
- For example, when you push a book across a table, the work you do overcomes the resistance caused by the contact between the book and the table.
- Likewise, when you lift this book, you do work to overcome the gravitational attraction.
- Kinetic energy is the capacity to do work resulting from the motion of an object.
- The amount of an object's kinetic energy is related to its mass and its velocity.
- If two objects are moving at the same velocity, the one with the greater mass ill have a greater capacity to do work and thus a greater kinetic energy.
- If two objects have equal mass but different velocities, the one with the greater velocity has the greater kinetic energy.
- Energy can be transferred from object to another.
- The Law of Conservation of Energy states that energy can be neither created not destroyed, but it can be transferred from one system to another and changed from one form to another.
- For example, a coin starts out resting in your hand. After you flip it, sending it moving up into the air, it has the kinetic energy that it did not have before it as flipped. The coin got their energy from your moving thumb.
- Potential energy is the stored form of energy an object possesses by virtue of its position or state.
- There are many kinds of potential energy. Ex. alkaline battery
Units of Energy
- The SI unit for energy is the joule (J), but another common one is calorie (c).
- It is necessary to increase the temperature of 1 gram of water from 1 Celsius degree.
- 4.184 J = 1 cal
- Exothermic is a change that leads to heat energy being released from the system to the surroundings.
- Endothermic is the change that leads a system to absorb heat energy from the surroundings.
Entropy and Enthalpy
- enthalpy: heat energy
- entropy: measure of disorder
Human Activities and Greenhouse Gases
Fossil fuel combustion produces many unwanted waste products, including oxides of nitrogen and sulfur, and carbon dioxide (CO2). Before industrialization occurred, atmospheric carbon dioxide levels are estimated to have been around 280 parts per million by volume in air. In 1957 Charles Keeling measured a carbon dioxide concentration of 318 parts per million in air over Mauna Loa volcano in Hawaii. Since that time, carbon dioxide concentrations have shown a continued upward trend, with a mean global carbon dioxide growth rate from 1981 (global average concentration of about 340 parts per million by volume) to 1996 (global average concentration of about 363 parts per million by volume) estimated to be around 1.4 parts per million by volume. Because carbon dioxide is a greenhouse gas, it is widely believed by most scientists and many nonscientists that any prolonged, substantial increase in the atmospheric concentration of carbon dioxide will contribute to global warming. Some estimates suggest that carbon dioxide emissions from the mid-nineteenth century through the end of the twentieth century have already increased the global tropospheric heating rate.
With the increase in “greenhouse gases” such as carbon monoxide in Earth’s atmosphere, the sun’s heat becomes trapped (straight arrows), leaving less to escape back into space (wavy arrows); as a result, the overall temperature of the planet rises.Methane, also a greenhouse gas, has increased from 1.61 parts per million by volume in 1983 to 1.73 parts per million by volume in 1996. Humans have increased the acreage of rice paddies and the size of cattle herds, both major sources of atmospheric methane. Leakage and deliberate venting of methane during mining operations contribute significant amounts of methane to the atmosphere. In addition, methane is a product of incomplete combustion. Nitrous oxide, another greenhouse gas, is also produced as a by-product of combustion. Chlorofluorocarbons such as freon and halon, which are completely human-made contaminants with relatively long atmospheric half-lives, are much more potent greenhouse gases than carbon dioxide and methane.
Although carbon dioxide, methane, nitrogen oxides, freon, and halon all trap infrared radiation that would otherwise escape into space, the greatest effects on climate change would result from changes in the amount of water vapor in the atmosphere and the amount and type of clouds worldwide. Water vapor is itself a greenhouse gas; many climate models factor in feedbacks from a temperature rise caused by other greenhouse gases favoring higher global concentrations of atmospheric water vapor, which adds to global warming. However, most experts predict that worldwide increases in water vapor concentrations in the atmosphere would be coupled with increased cloudiness, which would probably result in greater reflection of solar radiation back to space. This would have a cooling effect.
When coal containing sulfur is burned, various sulfur oxides are formed, which, once released into the atmosphere, are converted to sulfuric acid (SO4) aerosol. Because of their optical properties, sulfate aerosols reflect solar radiation back into space. Some scientists have postulated that sulfate aerosols produced by burning of fossil fuels have caused globalcooling at a sufficient rate to cancel the global warming that would be expected to have occurred with the release of carbon dioxide from that same burning.
"Climate Change and Global Warming." Encyclopedia of Environmental Issues. 1999. eLibrary Science. Web. 27 Feb 2013.
With the increase in “greenhouse gases” such as carbon monoxide in Earth’s atmosphere, the sun’s heat becomes trapped (straight arrows), leaving less to escape back into space (wavy arrows); as a result, the overall temperature of the planet rises.Methane, also a greenhouse gas, has increased from 1.61 parts per million by volume in 1983 to 1.73 parts per million by volume in 1996. Humans have increased the acreage of rice paddies and the size of cattle herds, both major sources of atmospheric methane. Leakage and deliberate venting of methane during mining operations contribute significant amounts of methane to the atmosphere. In addition, methane is a product of incomplete combustion. Nitrous oxide, another greenhouse gas, is also produced as a by-product of combustion. Chlorofluorocarbons such as freon and halon, which are completely human-made contaminants with relatively long atmospheric half-lives, are much more potent greenhouse gases than carbon dioxide and methane.
Although carbon dioxide, methane, nitrogen oxides, freon, and halon all trap infrared radiation that would otherwise escape into space, the greatest effects on climate change would result from changes in the amount of water vapor in the atmosphere and the amount and type of clouds worldwide. Water vapor is itself a greenhouse gas; many climate models factor in feedbacks from a temperature rise caused by other greenhouse gases favoring higher global concentrations of atmospheric water vapor, which adds to global warming. However, most experts predict that worldwide increases in water vapor concentrations in the atmosphere would be coupled with increased cloudiness, which would probably result in greater reflection of solar radiation back to space. This would have a cooling effect.
When coal containing sulfur is burned, various sulfur oxides are formed, which, once released into the atmosphere, are converted to sulfuric acid (SO4) aerosol. Because of their optical properties, sulfate aerosols reflect solar radiation back into space. Some scientists have postulated that sulfate aerosols produced by burning of fossil fuels have caused globalcooling at a sufficient rate to cancel the global warming that would be expected to have occurred with the release of carbon dioxide from that same burning.
"Climate Change and Global Warming." Encyclopedia of Environmental Issues. 1999. eLibrary Science. Web. 27 Feb 2013.
Renewable Resources
Renewable resources are natural resources that are continuously produced or regenerated faster than they are depleted. Such resources are mainly derived from solar radiation, such as forest resources or renewable energy resources; however, water, soil, wildlife, plants, and wetlands can also be considered renewable resources.
Renewable energy sources, such as wind energy and hydroelectricity, are mainly derived from solar energy in one form or another. Direct solar radiation is usually converted into heat, which can be used for such purposes as heating homes or water. Solar water heating has been used in the southern United States since at least the early twentieth century. In mild climates such as southern Florida, it can easily furnish all the hot water requirements of a typical home. It has also been widely used in tropical countries throughout the world.
Passive solar heating is the heating of a building by solar radiation that enters the building through south-facing windows (north-facing in the Southern Hemisphere). A properly designed passive solar home must have enough interior heat capacity, usually in the form of concrete floors or walls, to be able to keep the house from overheating on a sunny day and to store excess heat for release at night. In many parts of North America and Europe, passive solar homes have proved to be economical, since the passive system is part of the house itself (its windows, walls, and floors) and thus adds little or no extra cost.
Active solar heating, in contrast to passive solar heating, uses air or liquid solar collectors that convert solar radiation into thermal energy, which is stored and distributed using a mechanical system (fans or pumps). Active systems have fallen into disfavor because they are technically and economically inferior to passive solar systems.
Direct solar radiation can also be used to produce electricity by several different methods. Solar power towers use a field of movable mirrors to reflect sunlight onto a tower where the solar heat is used to generate electricity in place of a fossil or nuclear fuel. This concept has been tested in California and is technically, but not yet economically, feasible. Ocean thermal conversion plants generate electricity using the difference in temperature between the warm, solar-heated upper portions of the ocean and the colder water farther down. This concept has been partially tested, but no complete plant has yet been built.
Photovoltaic or solar cells are semiconductor devices that generate electricity directly from solar (or other electromagnetic) radiation. Originally developed for artificial satellites after World War II, photovoltaic cells work well and are already in use for many purposes, such as solar calculators and radios, patio lights, electric fences, traffic signal controls, and corrosion prevention on metal bridges. However, they are not yet cheap enough to be economical for generating electricity in homes.
A less direct type of renewable solar energy is hydroelectricity—electricity generated by water turbines that are turned by water flowing down a river or dropping from a dammed water reservoir. The kinetic energy of the moving water is derived from gravitational potential energy of water at greater heights, and that energy is ultimately derived from solar radiation that evaporated the water from the oceans, allowing it to rain down in the mountains. An interesting type of hydroelectric plant is one that derives its energy from rising and falling tides. The only major example of such a tidalenergy power plant is on the Rance River in northern France. An older form of water power was the waterwheel used by millers until well into the nineteenth century.
Wind energy is also a renewable solar energy resource because it is the uneven heating of the earth’s land and water areas by the sun that causes winds. Wind energy has long been used as an energy source: It powered the sailing ships that explored the globe, and it powered the windmills used in Asia and Europe since the Middle Ages to grind grain and pump water. Since the 1920’s wind turbines have been used to generate electricity in rural areas of the United States, and they are now being used by some electric utilities.
"Renewable Resources." Encyclopedia of Environmental Issues. 1999. eLibrary Science. Web. 27 Feb 2013.
Renewable energy sources, such as wind energy and hydroelectricity, are mainly derived from solar energy in one form or another. Direct solar radiation is usually converted into heat, which can be used for such purposes as heating homes or water. Solar water heating has been used in the southern United States since at least the early twentieth century. In mild climates such as southern Florida, it can easily furnish all the hot water requirements of a typical home. It has also been widely used in tropical countries throughout the world.
Passive solar heating is the heating of a building by solar radiation that enters the building through south-facing windows (north-facing in the Southern Hemisphere). A properly designed passive solar home must have enough interior heat capacity, usually in the form of concrete floors or walls, to be able to keep the house from overheating on a sunny day and to store excess heat for release at night. In many parts of North America and Europe, passive solar homes have proved to be economical, since the passive system is part of the house itself (its windows, walls, and floors) and thus adds little or no extra cost.
Active solar heating, in contrast to passive solar heating, uses air or liquid solar collectors that convert solar radiation into thermal energy, which is stored and distributed using a mechanical system (fans or pumps). Active systems have fallen into disfavor because they are technically and economically inferior to passive solar systems.
Direct solar radiation can also be used to produce electricity by several different methods. Solar power towers use a field of movable mirrors to reflect sunlight onto a tower where the solar heat is used to generate electricity in place of a fossil or nuclear fuel. This concept has been tested in California and is technically, but not yet economically, feasible. Ocean thermal conversion plants generate electricity using the difference in temperature between the warm, solar-heated upper portions of the ocean and the colder water farther down. This concept has been partially tested, but no complete plant has yet been built.
Photovoltaic or solar cells are semiconductor devices that generate electricity directly from solar (or other electromagnetic) radiation. Originally developed for artificial satellites after World War II, photovoltaic cells work well and are already in use for many purposes, such as solar calculators and radios, patio lights, electric fences, traffic signal controls, and corrosion prevention on metal bridges. However, they are not yet cheap enough to be economical for generating electricity in homes.
A less direct type of renewable solar energy is hydroelectricity—electricity generated by water turbines that are turned by water flowing down a river or dropping from a dammed water reservoir. The kinetic energy of the moving water is derived from gravitational potential energy of water at greater heights, and that energy is ultimately derived from solar radiation that evaporated the water from the oceans, allowing it to rain down in the mountains. An interesting type of hydroelectric plant is one that derives its energy from rising and falling tides. The only major example of such a tidalenergy power plant is on the Rance River in northern France. An older form of water power was the waterwheel used by millers until well into the nineteenth century.
Wind energy is also a renewable solar energy resource because it is the uneven heating of the earth’s land and water areas by the sun that causes winds. Wind energy has long been used as an energy source: It powered the sailing ships that explored the globe, and it powered the windmills used in Asia and Europe since the Middle Ages to grind grain and pump water. Since the 1920’s wind turbines have been used to generate electricity in rural areas of the United States, and they are now being used by some electric utilities.
"Renewable Resources." Encyclopedia of Environmental Issues. 1999. eLibrary Science. Web. 27 Feb 2013.