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There are four types of evidence of a chemical reaction. They are:
color changes, formation of a precipitate, formation of a gas, and
temperature change.
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Color Changes: The reactant changes to a different colored product during a chemical reaction.
Example: When gray iron, the reactant, rusts, it becomes a brown product.
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Formation of a Precipitate: A solid product occurs when chemicals in two liquids react.
Example: Sea creatures often release a liquid that reacts with the ocean water, forming a seashell.
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| Formation of a Gas: A gas can be formed when two substances react.
Example: When mixed with stomach acid, antacid pills form a gas. |
Temperature Change: Many chemical reactions involve a temperature
change. Sometimes, it is visible, like a flame, and other times, it is
not.
Example: Concrete sometimes gets warm before it hardens, which is due
to a chemical reaction.
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