Chapter 5: Stored Energy and Batteries

Energy cannot be created or destroyed, but it can be saved in various forms. One way to store it is in the form of chemical energy in a battery. When connected in a circuit, a battery can produce electricity.

If you look at a battery, it will have two ends -- a positive terminal and a negative terminal. If you connect the two terminals with wire, a circuit is formed. Electrons will flow through the wire and a current of electricity is produced.

Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons. Batteries can be stored for a long time and still work because the chemical process doesn't start until the electrons flow from the negative to the positive terminals through a circuit.

How the Chemical Reaction Takes Place in a Battery

A very simple modern battery is the zinc-carbon battery, called the carbon battery for short.

This battery contains acidic material within and a rod of zinc down the center. Here's where knowing a little bit of chemistry helps.

SIDEBAR As we read in Chapter 1, Alessandro Volta created the first battery (also see our "Super Scientists" page). Volta called his battery the Voltaic Pile. He stacked alternating layers of zinc, cardboard soaked in salt water and silver. It looked like this: If you attach a wire to the top and bottom of the pile, you create an electric current because of the flow of electrons. Adding another layer will increase the amount of electricity produced by the pile.

When zinc is inserted into an acid, the acid begins to eat away at the zinc, releasing hydrogen gas and heat energy. The acid molecules break up into its components: usually hydrogen and other atoms. The process releases electrons from the

Zinc atoms that combine with hydrogen ions in the acid to create the hydrogen gas.

If a rod of carbon is inserted into the acid, the acid does nothing to it.

But if you connect the carbon rod to the zinc rod with a wire, creating a circuit, electrons will begin to flow through the wire and combine with hydrogen on the carbon rod. This still releases a little bit of hydrogen gas but it makes less heat. Some of that heat energy is the energy that is flowing through the circuit.

The energy in that circuit can now light a light bulb in a flashlight or turn a small motor. Depending on the size of the battery, it can even start an automobile.

Eventually, the zinc rod is completely dissolved by the acid in the battery, and the battery can no longer be used.

Different Types of Batteries

Different types of batteries use different types of chemicals and chemical reactions. Some of the more common types of batteries are:

• Alkaline battery -- Used in Duracell¨ and Energizer¨ and other alkaline batteries. The electrodes are zinc and manganese-oxide. The electrolyte is an alkaline paste.
• Lead-acid battery -- These are used in automobiles. The electrodes are made of lead and lead-oxide with a strong acid as the electrolyte.
• Lithium battery -- These batteries are used in cameras for the flash bulb. They are made with lithium, lithium-iodide and lead-iodide. They can supply surges of electricity for the flash.
• Lithium-ion battery -- These batteries are found in laptop computers, cell phones and other high-use portable equipment.
• Nickel-cadmium or NiCad battery -- The electrodes are nickel-hydroxide and cadmium. The electrolyte is potassium-hydroxide.
• Zinc-carbon battery or standard carbon battery -- Zinc and carbon are used in all regular or standard AA, C and D dry-cell batteries. The electrodes are made of zinc and carbon, with a paste of acidic materials between them serving as the electrolyte.

Food - Another Method of Storing Energy

Batteries store energy in a chemical process, but there are other ways of storing energy. Consider the "food chain" on our planet.

Plants, like grass in a meadow, convert the sun's energy through photosynthesis into stored chemical energy. This energy is stored in the plant cells is used by the plant to grow, repair itself and reproduce itself.

Cows and other animals eat the energy stored in the grass or grain and convert that energy into stored energy in their bodies. When we eat meat and other animal products, we in turn, store that energy in our own bodies. We use the stored energy to walk, run, ride a bike or even read a page on the Internet.

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READ MORE ABOUT IT!

Here are some additional websites to check out.

• Alex's Electronic Resource Library: Batteries (www.iserv.net/~alexx/lib/componet.htm)
  
• Battery Facts: Memory Effect (www.batterybank.com/page18.html)
  
• BBC: How Do Batteries Work? (www.open2.net/science/roughscience/library/batteries.htm)
  
• Energizer Learning Center (www.energizer.com/learning/)
  
• How Stuff Works - battery http://www.howstuffworks.com/battery.htm)
  
• Official Lemon-Power Website! - using lemons to power stuff! (www.autopenhosting.org/lemon/index.html)
  
• Rayovac/Walmart Science Kit Page - Info on batteries and how to make your own battery
  
• ScienceNet: How do rechargeable batteries work? (www.sciencenet.org.uk/database/Physics/9812/p01313d.html)
  
• Valence Technology Battery Education (www.valence.com/BatteryEducation.asp)