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Chemical Reactions

Chemical Reactions. 8.5E Investigate how evidence of chemical reactions indicates that new substances with different properties are formed. . How is a chemical change different from a physical change?.

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Chemical Reactions

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  1. Chemical Reactions 8.5E Investigate how evidence of chemical reactions indicates that new substances with different properties are formed.

  2. How is a chemical change different from a physical change? • Matter can be changed in many ways, but all of these changes can be classified as either a chemical change or physical change.

  3. What is a chemical reaction? • A change in matter that results in a new substance with different chemical and physical properties than the original substance. • Identify the chemical changes: • Glass breaking • Rusting metal • Burning toast • Cutting grass • Fireworks exploding • Melting butter • Digesting food ✓ ✓ ✓ ✓

  4. What are the signs that a chemical reaction has occurred? The best way to identify that a chemical reaction has occurred is the formation of a new substance with different properties. Here are some clues: • Color Change • Gas Production • Change in Energy • Precipitate formation

  5. When does color change indicate that a chemical reaction has occurred? • When a color change is unexpected. For example, you would expect to get a green liquid when you mix a blue and yellow liquid. But getting a green liquid from combining two clear liquids is unexpected. • Examples of chemical reactions that result in color change: • Bleaching clothes • Dying hair • Burning toast

  6. What are some examples of gas production during a chemical reaction? • Bubbles, fizzing, foaming, releasing a vapor (not boiling) • Burning wood – the smoke is a new product made of carbon dioxide and water vapor. • Combining vinegar and baking soda – bubbles and fizzing releasing carbon dioxide gas

  7. What does “a change in energy mean?” • A change in energy in a chemical reaction means that energy is either absorbed or released during a chemical reaction. • It is very common for energy in the form of heat (thermal energy) to be absorbed or released during a chemical reaction. This results in either a temperature increase or decrease. • Sometimes the change in energy is light energy being absorbed or released. Photosynthesis is an example of a reaction that absorbs light energy. A glow stick is an example of a chemical reaction releasing light energy.

  8. What is a precipitate? • A precipitate is a solid that forms during a chemical reaction between two liquids.

  9. Most Importantly…. • Always ask “Is it a new substance with different properties?”

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