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Unformatted text preview: Chapter 4 Notes—Energy, Chemistry, and Society 26 March 2008 4.1—Energy, Work and Heat-Energy is the capacity to do work. Work is done when movement occurs against a restraining force. Mathematically, work is equal to the force multiplied by the distance over which the motion occurs.-Heat is energy that flows from a hotter to a colder object.-Temperature is a property that determined the direction of heat flow.-Heat is a consequence of motion at the molecular level. Temperature is a statistical measure of the average speed of that motion. Hence, temperature rises as the amount of heat energy in a body decreases.-One joule (1 J) is approximately equal to the energy required for one beat of a human heart.-Originally, the calorie was defined as the amount of heat necessary to raise the temperature of exactly one gram of water by one degree Celsius. It has been redefined as exactly 4.184 J. Calories are perhaps most familiar when used to express the energy released when food are metabolized. 4.2—Energy Transformation-Essentially al the fuels we will consider in this chapter—coal, oil, alcohol, and garbage—give up their energy through combustion.-Energy stored in the chemical bonds of the fuel molecules is released during combustion. The first law of thermodynamics, also called the law of conservation of energy and mass, states that energy is neither created nor destroyed. Energy often changed forms as it did in the combustion reaction, but the energy of the universe is constant.-For the most part, hear is not the form in which the energy is ultimately used. The industrialization of the world’s economy began with the invention of devices to convert heat to work. The heat from burning wood or coal was used to vaporize water, which in turn was used to drive pistons and turbines. The resulting mechanical energy was used to power pumps, mills, looms, boats, and trains.-Today, most of the electrical energy produced in the United Stated is generated by the descendants of those early steam engines. -Heat from the burning fuel is used to boil water, usually under high pressure. The elevated pressure serves two purposes: it raises the boiling point of the water and it compresses the water vapor. The hot, high pressure vapor is directed at the find of a turbine. As the gas expands and cools, it gives up some of its energy to the turbine, causing it to spin like a pinwheel in the wind. The shaft of the turbine is connected to a large coil of wire that rotates within a magnetic field. The turning of this dynamo generates an electric a large coil of wire that rotates within a magnetic field....
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This note was uploaded on 04/16/2008 for the course CHEM 1301 taught by Professor Babilli during the Spring '07 term at SMU.
- Spring '07