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big city vs small town

By ksa_101 Oct 05, 2013 2130 Words
Matter and Energy
Learning Objectives
Understand the general concepts of matter and energy-why are these entities important to environmental scientists? Be able to define and give examples of the three laws governing matter and energy-how do these laws affect our understanding of matter/energy quantity and quality Be able to differentiate between potential and kinetic energy Be able to discuss the concept of entropy and how this process affects all living things Check out the chemistry review if you feel you need some additional chemistry background for this section I. One important thing about systems and living things: Life obeys physical laws.

Drink some water, eat some food, run to class. The two things that connect these activities and other aspects of life on earth are matter and energy. Matter has mass and occupies space: it is the stuff you and everything else is made of. Matter comes in a variety of forms. We call these different unique types of matter elements. An atom is the smallest unit of an element that has all of the properties of that element. There are 92 naturally occurring elements in nature. These different forms of matter differ uniquely in their physical and chemical properties: carbon (C) and hydrogen (H) differ in their size, reactiveness with other atoms, and other physical and chemical properties. An element is a substance that cannot be broken down to other substances by ordinary chemical means. An element can be combined with another to make a compound. For instance, hydrogen combines with oxygen to produce water. Scientists use symbols (hydrogen=H, oxygen=O) as a kind of short-hand for describing compounds. For example H2O is mean water is comprised of 2 toms of hydrogen and one atom of oxygen II. Energy is a more elusive concept. Formally, it is defined as the ability (or capacity) to do work Work is the product of force and distance. When you are walking up the Hill, you are doing work by applying muscles (force) to move up the Hill (distance). Energy is what you and all living things use to move matter around and to change matter from one form to another. Energy is used to grow your food, to keep you alive (metabolism), to move you from one place to another, and to warm and cool the buildings in which you work and live. The uses and transformations of matter and energy are governed by certain scientific laws, which unlike the laws people enact, cannot be broken. III. There are three physical laws governing matter and energy that are important to us. A) Law of conservation of matter

B) First law of energy (first law of thermodynamics)
C) Second law of energy (second law of thermodynamics)
A. Law of Conservation of Matter: (everything must go somewhere) We talk about consuming, or using up material resources, but actually we don't consume any matter. We only borrow some of the earth's resources for a while C taking them from the earth, carrying them to another part of the globe, processing them, using them, and then discarding, reusing, or recycling them. In the process of using matter we may change it to another form, but in every case we neither create nor destroy any measurable amount of matter. This results from the law of conservation of matter: In any physical or chemical change, matter is neither created nor destroyed but merely changed from one form to another. When you throw away something, remember there is no "away." Everything we think we have thrown away is still here with us in one form or another.  How does this affect environmental science ? Although we can certainly make the environment cleaner, the law of conservation of matter says we will always be faced with pollution of some sort. This means that we musttrade-off one form of pollution for another. This trade-off involves making controversial scientific, political, economic, and ethical judgments about what is a dangerous pollution level, to what degree a pollutant must be controlled, and what amount of money we are willing to pay to reduce the amount of a pollutant to a harmless level.   B. The First Law of Energy (First Law of thermodynamics): You can't get something for nothing  You encounter energy in many forms: mechanical, chemical (food and fuel), electrical, nuclear, heat, and radiant (such as light). Scientists usually classify most forms of energy as either potential or kinetic energy.  1) Kinetic energy is the energy that matter has because of its motion and mass. A moving car, falling rock, and the flow of electrons or charged particles called electrical energy are all examples of kinetic energy.  The amount of kinetic energy matter has depends on both its mass and its velocity (speed). Because of its velocity a bullet fired from a gun can cause more damage that one thrown by hand; and a bowling ball dropped on your foot does more damage that a pool ball.  2) Potential energy: The energy stored by an object as a result of its position or the position of its parts is called potential energy. A rock held in your hand, a bowl of cereal, a stick of dynamite, and a tank of gas are all examples. The rock has stored (or potential) energy that can be released and converted into kinetic energy (in the form of mechanical energy and heat) if it is dropped. Doing work involves changing energy from one form to another.  a. When you lift an object, chemical energy (a form of potential energy) stored in the chemicals obtained from your digested food is converted into the mechanical energy (kinetic) used to move your arm and the object upward and into heat given off by your body b. In an automobile engine, the che into electrical energy and heat (low grade form of kinetic energy. c. In an electric power plant, chemical energy from fossil fuels (potential) or nuclear energy from uranium nuclear fuel (potential) is converted into a combination of mechanical energy and heat. The mechanical energy is used to spin the turbine that converts the mechanical energy into electrical energy and more heat. When the electrical energy oscillates through the filament wires in an ordinary light bulb, it is converted into light and still more heat. Note that in all of these transformations, some energy is always lost as heat that flows into the surrounding environment. 3) Energy changes: What energy changes occur when you drop a rock? Because of its higher position, the rock in your hand has a higher potential energy than the same rock at rest on the ground. When you drop the rock and it hits and eventually rests on the ground, the rock now has a much lower potential energy. Has the amount of energy changed (i.e., the rock lost energy - where did it go?) At first glance it seems so. But according to the first law of conservation of energy, in any ordinary physical or chemical process is neither created nor destroyed but merely change from one form to another.  The energy lost by a system or collection of mater under study (in this instance, the rock) must equal the energy gained by the surroundings or environment (in this instance, air molecules pushed out of the way, and soil particles moved by the impact of the rock). This energy law holds for all systems, living and nonliving.  Let's look at what really happens. As the rock drops, its potential energy is changed into kinetic energy C both its own and that of the air through which it passes. The friction created when the rock is drops through the air causes air molecules in the air to move faster, so their average temperature rises. This means that some of the rock's original potential energy has been transferred to the air as heat. When the rock hits the ground more of its mechanical energy is transferred to particles of soil. The energy lost by the rock (system) is exactly equal to the energy gained by its surroundings. Scientists have never seen an instance where energy input does not equal energy output.   C. Second Law of Energy (Second law of thermodynamics): You can't break even  Energy quality: Because according to the first energy law energy can neither be created nor destroyed, you might think there will always be enough energy. Yet when you fill a car's tank with gasoline and drive around something is lost. If it isn't energy, what is it? The second law of energy, also known as the second law of thermodynamics provides the answer to this question.  Energy varies in its quality or ability to do useful work. For useful work to occur energy must move or flow from a level of high-quality (more concentrated) energy to a level of lower-quality (less concentrated) energy. The chemical potential energy concentrated in a lump or coal or a tank of gasoline and the concentrated heat energy at a high temperature are forms of high-quality energy. Because the energy in gasoline or coal is concentrated, they have the ability to perform useful work in moving or changing matter . In contrast, less concentrated heat energy at a low temperature has little remaining ability to perform useful work.  Over the years, after investigating millions of conversions of energy from one form to another, scientists have found that some of the energy is always degraded to a more dispersed and less useful form, usually as heat given off at a low temperature to the surroundings.    

In an internal combustion automobile engine, only about 20% of the high-quality chemical energy available in the gasoline is converted to mechanical energy used to propel the car; the remaining 80% is degraded to low-quality heat that is released into the environment. In addition, about 50% of the mechanical energy produced is also degraded to low-quality heat energy through friction, so that 90% of the energy in gasoline is wasted and not used to move the car.    

When electrical energy oscillates through the filament wires in an ordinary light bulb, it is converted into a mixture of about 5% useful radiant energy (light) and 95% low-quality heat.    
It is interesting to note that much of modern civilization is built around the internal combustion engine and the incandescent light that, respectively, waste 90 and 95% of their initial energy input. Some of this waste is due to the energy-quality tax automatically exacted as a result of the second energy law and some is due to technological designs that waste more energy that necessary.    

Most energy exchange processes occur like this (high quality energy to low quality) but there is one VERY IMPORTANT exception: the conversion of solar energy to chemical energy in food by plants and some bacteria.Photosynthesis converts radiant energy (light) from the sun into high-quality chemical energy (stored in the plant in the form of sugar molecules) and low-quality heat energy. If you eat plant food [like spinach], its high-quality chemical energy is transformed within your body to high-quality mechanical energy, used to move your muscles and to perform other life processes, and low-quality heat energy. The process of breaking down food such as sugars to simpler molecules, such as CO2 and water, releasing potential energy in the process, is called respiration. At each step, the low-quality heat flows into the environment. Without the action of plants and bacteria, life as we know it would not exist because animals have no way of turning the radiant energy from the sun into high energy (high quality) food.    

So, the first energy law governs the quantity of energy available from an energy conversion process, whereas the second energy law governs the quality of energy available. According to the first law we will never run out of energy, but according to the second law we can run out of high quality or useful energy.    

Not only can we not get something for nothing (the first law), we can't even break even in terms of energy quality (the second law)    
The second energy law also tells us that high-grade energy can never be used over again.    
We can recycle matter but we can never recycle high-quality energy.  Fuels and foods can be used only once to perform useful work. Once a piece of coal or a tank full of gasoline is burned, its high-quality potential energy is lost forever. This means that the net useful, or high-quality energy available from fossil fuels, uranium, or any concentrated energy source is even less than predicted by the first energy law.   

d. mical energy stored in the gasoline is converted into mechanical energy that propels the car and is eventually lost as heat (engine heat), friction of the tires with the ground, and energy imparted to the air as it is pushed out of the way by your car.

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