Q:

What are physical and chemical changes?

A:

Quick Answer

Physical changes do not produce new substances, but chemical changes do produce new substances. A physical change is concerned with states of matter. Melting, vaporization, freezing, sublimation and condensation are physical changes. Melting an ice cube is a physical change because the substance remains as water. Most physical changes are reversible. Crushing a can, boiling water, breaking glass, chopping wood, mixing sand and water, and shredding paper are physical changes.

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Full Answer

Chemical changes occur on the molecular level. The change produces a new substance. Chemical changes include combustion, synthesis, oxidation, neutralization and decomposition. For example, iron rusting is an instance of a chemical change. Food metabolism, burning wood, mixing and acid with a base, baking a cake and using a chemical battery are also examples of chemical changes.

A chemical change can be determined by evaluating if a reaction has occurred. A chemical reaction may have occurred if a change in light, heat, color, gas production, odor or sound is produced. If a precipitate develops, then a chemical change has occurred. An odor is a sign of a chemical change because it is evidence that decomposition is occurring. For example, a rotten egg produces an odor as it transforms into a new substance.

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Related Questions

  • Q:

    What are three examples of chemical changes?

    A:

    Examples of chemical changes include burning of wood, digestion of sugar, an exploding firecracker, reactions between salts and acids and lighting a matchstick. A chemical change involves changes at the atomic and molecular level.

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  • Q:

    How is energy involved in chemical and physical changes?

    A:

    Chemical changes within matter always use energy; physical changes sometimes use energy, though they use much less energy than chemical changes. Physical changes use energy to change the physical state of a substance. Chemical changes either release or absorb energy when changing a substance into a completely new one.

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  • Q:

    What does "chemical reaction" mean?

    A:

    The term "chemical reaction" refers to any process that changes a set of chemical substances to another. That is, the substances that are put into a chemical reaction are different, on a molecular level, from those that result.

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  • Q:

    Why do chemical reactions occur?

    A:

    Chemical reactions occur because different types of molecules interact with each other to create new substances. Many of these interactions happen naturally and are not man-made. When one molecule interacts with another one, a chemical reaction occurs due to the breaking of old bonds and the forming of new ones.

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