What are the signs that a chemical reaction has occurred?

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Chemical reactions occur when the atomic structure of reactants are rearranged to make new products. The following are signs that a chemical reaction may have occurred:

1.      The formation of a precipitate may indicate that a chemical reaction has occurred. Sometimes, when two liquids are mixed, a solid is formed and settles to the bottom of the solution. The solid that forms is called a precipitate.

2.      Color changes may indicate the presence of a chemical reaction.

3.      Temperature changes are often indicative of chemical reactions. For example, exothermic reaction release energy and make their surrounding feel warmer. Oppositely, endothermic reactions absorb heat energy and make their surrounding feel cooler.

4.      The production of odor may indicate that a chemical reaction has occurred. Just think of the smell of a campfire!

5.      Bubbles may be a sign that a chemical reaction has occurred. Although bubbles from a liquid are due to a physical change of state, bubbles can also be produced by a chemical reaction. For example, yeast in bread can produce bubbles of carbon dioxide that help the bread to rise.

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