How Batteries Illustrate the Law of Conservation of Energy


Every high school physics student learns the law of conservation of energy. Often times, energy conservation is the first thing discussed on day one. That makes sense, given that physics is the study of energy. At any rate, the law of conservation of energy is considered an absolute law. It does not change.

The law is easily observed by looking at how batteries work. Despite what you may believe, batteries do not actually store electricity. They generate electricity as a result of a chemical reaction taking place inside. That reaction, along with what it takes to charge and discharge a battery, perfectly illustrates the law of conservation of energy.

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1. More About the Conservation of Energy

The law of the conservation of energy dictates that energy can neither be created nor destroyed. It can only change forms, thus conserving its existence when transformation occurs. Our understanding of the universe is built on this law. Physicists have spent their entire careers trying to understand why the law exists but to no avail.

Some might dispute energy conservation based on personal observation. For example, a physics student may protest due to his experience with fire. He knows that a spark resulting in fire generates heat energy. Said energy was not present prior to the spark. Or was it?

Understanding the difference between potential and kinetic energy is fundamental to understanding the law of the conservation of energy. The heat energy produced by fire existed before the fire did. It just existed in a couple of different forms. In those forms, it was potential energy. It became kinetic energy once the flame appeared.

2. How Batteries Work

The mechanism behind how batteries work is a better illustration of energy conservation because it is more tangible than fire. Consider a USB rechargeable battery from Salt Lake City’s Pale Blue Earth. You are looking at a lithium-ion battery that stores potential energy.

Pale Blue Earth explains that each one of its batteries consists of a case that contains an anode, a cathode, an electrolyte, and lithium ions. To charge the battery, you run current through it – from positive end to negative. This forces the ions to move through the electrolyte and stack up at the negative end (the cathode).

Installing a charged battery into a device completes the electrical connection between anode (the positive end) and cathode. This forces the ions back through the electrolyte toward the anode. As they move through the electrolyte, they trigger a chemical reaction that generates electricity.

3. Potential Energy in the Ions

It is clear that batteries do not store electricity. They store potential energy in the ions within. That potential is just waiting to be released, which is what happens when ions trigger the chemical reaction in the electrolyte. It is the chemical reaction that creates the electricity, transforming potential energy into kinetic energy.

In simple terms, potential energy is energy at rest. Kinetic energy is energy in motion. Kinetic energy is measurable in the sense that it does actual work. Potential energy does not. It remains inert until it is transformed into kinetic energy.

Discharging a battery does not create energy. It just transforms potential energy stored in lithium ions into electricity. Likewise, charging a battery does not destroy energy. It converts electricity into potential energy stored in the same ions.

Batteries are an excellent illustration of the law of conservation of energy. No matter how you slice it, energy can neither be created nor destroyed. It can only be transformed into other forms. Is there anything else in the universe that operates this way?