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Energy Tutorial:
What is energy?
What are the consequences?
Is it conserved?

chemistry in a new light As mentioned before, chemistry can be studied by concentrating on the 3 areas of focus. This chapter on thermochemistry mostly focuses on the Force & Energy aspect of chemistry. There's also quite a bit of Mathematics focus as well.
What is Energy?
One way to define energy is by observation. If you see something that doesn't happen on its own, then there must be some energy being expended. For example, cars don't go up hill on their own, so there must be some energy getting used. Coming downhill, however, we could see that happening without any energy being used.
Like the car going up hill, anything that gets lifted against gravity requires some energy. Fortunately, this energy has the potential to be used again. For example, the energy to raise the skiers up the mountain will be used to propel the skiers down the slopes.
We can think of just two types of energy, one doing work, and the other waiting to do work.

Freedom Train at Houston Union Station, February 1976 - photo © Gary Morris (Used with Permission)
When it's doing work, we see it pushing or pulling, glowing, or changing the temperature. This train is using energy in three ways because it's pulling cars, heating up the surrounding air, and giving off light.
Energy that is waiting to do work (has to the potential for work) is called potential energy and is recognized in 3 ways:
    1) It sits above ground level
On the left is a pile driver. A weight (the driver) is lifted up to the top of the rig. The weight now has potential energy. As it falls the potential energy becomes kinetic energy (moving energy). When it strikes the post (pile/piling) at the bottom, the energy is used to drive the post farther into the ground. It's a smart way to deliver a lot of force. Wrestlers use the pile driver maneuver by lifting the opponent and letting gravity do the work as the opponent falls to the mat head first. On the right is Hoover dam. Lake Mead is held back by the dam. Lake Mead sits higher than the ground below the dam. This means the water in the lake has a lot of potential energy. This energy is tapped when water is allowed to flow downhill (kinetic energy) and spin turbines.
Energy is potential energy if: 2) Something is compressed in someway
A set mousetrap has a spring that has been compressed (or stretched), and it's sitting there ready to convert this potential energy to kinetic energy as the wire trap flips over to the other side. A tank of compressed air also possesses potential energy. If an air tool is attached that potential energy is used to push a piston that makes the air tool mechanism spin or vibrate.

Chemical energy is a type of potential energy. It's similar to raising objects against gravity (like the pile driver) except instead of moving objects against the attraction of gravity, it is moving objects against the attraction of plus and minus charges. To illustrate this, let's look at the simplest of elements, hydrogen....

The hydrogen atom consists of one proton (+) and one electron (-). The proton sits in the center (nucleus) of the atom. The proton is 2,000 times heavier than the electron. The electron is lightweight and very mobile. The diagram shows the electron as a sphere orbiting the nucleus. This is a simplistic view of an electron. Electrons are more cloud-like than ball-like. If an electron is moved farther away from the proton it takes energy because they are attracted to each other (like gravity). The farther away the electron has been moved away from the proton, the more energy it takes, and the more potential energy stored in the electron. When the electron drops back closer to the proton, it will convert that potential energy to light energy. The light energy can be in the form of infrared, visible, ultraviolet, or even X-ray light.
Chemical energy is stored in fuels like methane (natural gas) and gasoline. Let's see how methane combining with oxygen (combustion) gives up this type of potential energy.
When methane collides with oxygen at high speeds (caused by flame or spark), there's a rearrangement of the atoms. Two of the oxygen atoms will combine with the four hydrogen (H) atoms to form two water molecules (H2O). The other two oxygen atoms will combine with methane's carbon atom to form carbon dioxide. Why does this give off energy?

Below is the same diagram as above, except all of the protons and electrons that hydrogen, carbon, and oxygen have are shown. Hydrogen has one proton and one electron. Carbon has six protons and six electrons. Oxygen has 8 protons and 8 electrons. Remember the electrons are all being pulled on by the protons (kind of like Earth pulling on objects on the Earth).

The reason energy is released during rearrangement is that overall, the electrons are closer to the protons than they were originally. Remember when the electron on the hydrogen atom goes from farther away to closer, energy is released? Same thing is happening here except several electrons are involved. This "moving" closer to the nucleus means that some of the potential energy gets converted to light. The light is the visible light you see in the picture plus a great deal of infrared light, which is the heat you feel radiating from the flame.
What are the consequences of using energy?

The positive consequence is that we have the energy to make the products we want, travel to where we want, keep ourselves warm or cool, and to power all of the appliances and devices we like in our lives.

The negative consequences can be categorized as inescapable consequences and unfortunate consequences.

INESCAPABLE CONSEQUENCES: The laws of physics cannot be broken. One such law states the impossibility of ever making a perpetual motion machine, which is a machine that does work without any extra energy going into it. In the beginning of the industrial revolution, attention focused on the efficiency of machines. Factory owners wanted machines that could either provide work without added energy or at least do work with 100% efficiency. The result of the research was that neither was possible.

INESCAPABLE CONSEQUENCES: The picture on the left is a perpetual motion design. The water in the upper trough pours out on the water wheel on the right. The water wheel turns and the craftsman uses the left wheel for grinding. The tilted corkscrew apparatus is called the Archimedes screw which has the ability to raise water if the screw turns. The water wheel is suppose to provide power for the grinding wheel and the Archimedes screw that will replenish the water to the upper trough. Like all Perpetual Motion Designs, the flaw is that energy gets wasted as heat and there's never enough energy to keep the machine moving. In this example, the falling water will not have enough energy to turn wheels and gears and also pump the same amount of water back into the trough. The friction of the gears, water stirring, and water flowing will turn the potential energy of the raise water into heat.
INESCAPABLE CONSEQUENCES: Energy lost to heat is the final outcome of most anything we do with energy. Let's examine the above collage. The locomotive's purpose is to pull railroad cars from one place to another. However, nearly all of the energy it consumes goes to creating heat rather than moving the cargo. The steam engine or gas engine gets its power by heating a gas which expands and pushes on pistons which turns the wheels. The hot gas is then released (exhausted) so the pistons can return to their original position. The heat energy in the gas is now lost to the environment and no longer available to produce motion.

The weight lifter gets calories from food for energy to lift weight and maintain the body's metabolism. Only about 20% of the calories gets used by the body, the rest is lost to heat that escapes to the surrounding air. Even the energy in the raised weight will get lost when it hits the floor and warms the spot on the floor where it hits.

Electricity turns a piston in the air compressor to compress the air. The air gets quite hot as it has its molecules pushed closer. This heat energy could provide additional potential energy and pressure. However, the heat quickly dissipates through the metal walls of the compressor and is lost.

The wind generators get energy from the wind. However as the propellers turn, some energy is lost by friction of the bearings. As it generates electricity the friction of electrons traveling through the wires produces heat, which reduces the efficiency of the generator.

In other words, whenever we use energy, most, if not all, will be lost as heat that will no longer be available for doing useful work.

Losing so much energy to wasteful heat is depressing, but another law of physics is even more depressing...
If your life seems more chaotic as time goes by, don't feel alone. All of the universe is experiencing the same problem. When energy is used, more disorder (chaos) is created. In physics this is called "entropy," a measure of disorder often resulting from heat.
For example, the atoms of carbon and hydrogen in gasoline are lined up neatly in chains. After energy is released, the atoms are scattered and randomized. In other words, car exhaust has much higher entropy (disorder) than does gasoline and oxygen. In part because exhaust is a gas, which is bouncing in all directions. The extra heat causes even more random movements.
A warm homogenous soup. Because of this law which states all natural events lead to ever increasing disorder and wasted heat, a prediction of how the universe will end has been made. When the universe reaches uniform temperature and maximum randomness, we can no longer extract energy to do work or to survive. Don't worry. If true, it's still billions of years from now.
CONSERVATION OF ENERGY: Another inescapable consequence of energy is that energy is conserved. In other words, it doesn't go away, it just changes form. The simplest change of form to see is the pendulum. At the top of the pendulum swing, the ball comes to rest momentarily. At that point it has no kinetic energy, but it is at the maxi um height, so it has the maximum potential energy. At the bottom of the swing, it is moving the fastest (highest kinetic energy) but has the lowest potential energy. So the energy transforms from one to the other continually.

Friction convert Energies to Heat Energy:
In theory a pendulum should swing forever, but we all know that it will slow down and stop. That's because the movement of the pendulum is knocking against air molecules. The oxygen and nitrogen molecules in the air move about 1,000 miles per hour; however, when they strike the pendulum ball that's moving about 3 miles an hour, the air molecules get a boost of speed increase to about 1,003 miles per hour. So some of the kinetic energy of the pendulum is getting transferred to the air molecules. This extra speed in the air molecules actually means the air is now a little hotter. Also, there's some friction at the top where the wire is attached to the hook at the top. If a pendulum was swinging in a vacuum and the top hook was made with magnets that don't touch, then it would swing forever (at least a long time since you can't isolate the pendulum completely from the universe).


Greenhouse Gases and Pollution: Most of our energy comes from fossil fuels. The unfortunate consequences of this as you learned is that at a minimum it produces the two global warming (greenhouse) gases of water vapor and carbon dioxide. Since burning of fuels is done with air instead of just oxygen, we get nitrogen oxides forming. These are toxic and contribute to pollution. If the fossil fuels have impurities, such as sulfur, these impurities will end up in the air we breathe.

The energy in lightning splits oxygen molecules. These atoms of oxygen are very reactive and will immediately combine with other gases they encounter. If one bumps into nitrogen, it will form dinitrogen oxide. If it hits an oxygen molecule, it forms ozone. Both are toxic. Additionally, any sources of high voltage or electric sparks can do the same thing. Copy machines, laser printers, electric drills, spark plugs, bug zappers, vacuum cleaners, TV sets, and other similar devices can produce these toxic products. High energy can produce molecules of high energy, which are often dangerous.
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Last updated 10-28-09
Since Oct 29, 2009