Law of Conservation of Matter: Definition & Matter

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  • 0:01 Conservation in Chemistry
  • 1:30 Conservation of Mass
  • 2:38 Implications of the Law
  • 3:17 Lesson Summary
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Lesson Transcript
Instructor: Amy Lange

Amy has taught university-level earth science courses and has a PhD in Geology.

In this lesson, we'll learn the definition of the Law of Conservation of Mass, sometimes called the Conservation of Matter. This lesson explores the discovery of this important principle and covers a few examples of how it works.

Conservation in Chemistry

When you build fire during a camping trip, you pile up cut logs and some kindling and set flame to it. As the fire continues, the logs burn until you are eventually left with a small amount of ash and charred remains. What happened to your original logs? Did they just disappear?

According to the Law of Conservation, the magnitude of properties within a chemical system, such as mass, energy, or charge, remain unchanged during a chemical reaction. These properties may be exchanged between components of the system; however, the total amount in the system does not increase or decrease.

In our fire example, the burning wood is a chemical reaction. Wood is made of mainly carbon, hydrogen, and oxygen. When you burn wood, the heat from the fire breaks down the bonds between the elements. Hydrogen and oxygen are released into the air, while the carbon is left behind. Char, the black material left behind after wood is burnt, is mostly made of carbon.

Because we cannot see the gases that were released during the burning process, the mass of the end products appears smaller. But if we were able to measure the mass of the released carbon and oxygen plus the mass of the remaining char, we would find that the mass of all of these end products would be the same as our original wood. The form of the matter may be different, having transformed from solid wood to volatile gases and char, but the total mass of the end products are the same as what we started with.

Conservation of Mass

The Law of the Conservation of Mass was first realized by Antoine Lavoisier in the late 18th century. During this time, chemists of the day had noted that when metals were heated in open air, they were transformed into metal oxides and appeared to gain more mass. This process is similar to the formation of rust on iron when it is exposed to air and water.

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