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 Changes: Physical or Chemical?

Changes: Physical or Chemical?
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     edHelper's suggested reading level:   grades 5 to 8
     Flesch-Kincaid grade level:   7.03

Vocabulary
     challenging words:    orangey-red, photosynthesis, plasma, original, dioxide, electrical, burning, carbon, microscope, substance, vapor, heated, universe, rarely, account, ordinary

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Changes: Physical or Chemical?
By Cindy Grigg 		  
1     If you have studied atoms, you know that atoms are the building blocks of matter. Atoms are so small they cannot be seen with an ordinary microscope. Yet atoms make up everything in the universe. Atoms can combine with different atoms and make new substances. Substances can also break apart into separate atoms. These changes are called chemical changes or reactions. Chemical reactions happen when atoms gain, lose, or share electrons. What about when water freezes into ice? Do you think that's a chemical change?
 
2     When water freezes, it has changed states. You probably already know about the four states of matter. They are solid, liquid, gas, and plasma. Plasma is the fourth state of matter and is the most common state in the universe. However, it is rarely found on Earth. Plasma occurs as ball lightning and in stars. Water is a common substance that everyone has seen in its three states of matter. Water in its solid state is called ice. Water in the liquid state is just called water. Water as a gas is called water vapor. We can easily cause water to change states by changing its temperature. Water will freeze at 32 degrees Fahrenheit (0 Celsius). However, no chemical change has occurred. The atoms have not combined or broken apart to make a different substance; it is still water or H2O. When we heat water to a temperature of 212 F. or 100 Celsius, it will change into a gas called water vapor. Changes in states of matter are just physical changes.
 
3     Some more examples of physical changes are tearing paper into smaller pieces, sharpening your pencil, and stirring sugar into water. When you tear a piece of paper, it is still paper; it's just that the pieces are smaller. That is a physical change; a change you can easily see. When you sharpen your pencil, you have only caused a physical change. The sharpener has cut off some of the wood and maybe also some of the graphite, but the atoms of the wood and graphite have not changed chemically. You might think that the shavings you find inside the pencil sharpener are a new substance, but chemically they are not. They are still wood and graphite in smaller pieces than the original. When you stir sugar into water, you have only caused a physical change. The glass still contains water and sugar, but they have been mixed together. Is the sugar still there? Yes, you can taste it. This is only a physical change.

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