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Chemical Change: Signs & Evidence Video

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  • 0:04 What Is a Chemical Change?
  • 0:47 Signs and Evidence
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

From fireworks to a rusty penny, a lot of what we see involves a chemical change. Explore this lesson to learn about five different signs or evidence of chemical changes.

What Is a Chemical Change?

Have you ever looked into the sky and seen a beautiful set of fireworks on display? As amazing as fireworks are, we can also classify them as a type of chemical change. A series of chemical changes take place to produce those awesome fireworks we see.

By definition, a chemical change happens when the molecular identity of matter changes to an entirely new form. This change is irreversible; that is, there's no going back once a chemical change occurs. One way to remember this definition is to think of the term, a chemical reaction. That's right! This term should pop into your mind as a chemical change can also be called a chemical reaction.

Signs and Evidence

There are a variety of signs that may provide clues that a chemical change has entered the building. Let's look at the following five signs:

  1. Odor
  2. Energy change
  3. Gas bubbles
  4. Precipitate formation
  5. Color change

Odor

Have you ever witnessed the awful sight and smell of spoiled food? Before going bad, a chemical change must take place. The evidence of the chemical change in our food is the offensive smell. Not all the smells are bad however; the delicious smell of baking bread is due to chemical change as well.

Energy Change (Temperature and Light)

Remember that chemical changes tell you a chemical reaction is taking place. During chemical reactions, bonds that hold atoms together are constantly broken and formed, requiring or releasing energy. This energy directly affects temperature. For example, if we grab our flask and conduct a reaction where bonds are broken, we will see that a lot of energy is needed to break those bonds. By absorbing energy, don't be alarmed if the flask feels cold during the reaction.

When energy is released, it can sometimes be in the form of light, like in the glow emitted after you break a glow stick. When you're bending it, you're breaking a little tube inside that releases a liquid into the outer tube. The mix of chemicals together causes a chemical reaction that releases light as a byproduct.

Gas Bubbles

When a chemical reaction produces a gaseous product, this is an indication that a chemical change is occurring. Visually, this gaseous product is simply the presence of bubbles. This reaction can occur between two liquid solutions or even a solid added to a liquid solution. A great example can be the mixture of baking soda, a solid, with vinegar, a liquid. When you mix the two substances together, a chemical change occurs, and you can tell based on the appearance of lots and lots of bubbles.

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