When chemical reactions occur, heat may be given off or taken in from the environment. What changes occur during a reaction that can account for this fact?

Changes that might accompany a chemical reaction include color, appearance and production of new materials, for example, a gas. Mixing alone may not cause a chemical reaction to take place. While heat is often necessary to initiate a chemical reaction it is not always necessary. Chemical reactions are used to produce most of our energy.

Explanation:

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law of conservation of matter

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