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Chapter 7 in Review
Chemical reactions: One or more substances—either elements or compounds—change into a different substance.
Evidence of a chemical reaction: The only absolute evidence for a chemical reaction is chemical analysis showing that one or more substances have changed into another substance.
However, one or more of the following often accompanies a chemical reaction: a color change; the formation of a solid or precipitate; the formation of a gas; the emission of light; and the emission or absorption of heat.