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5.4 Physical and Chemical Changes

5.4 Physical and Chemical Changes. Learning Goals: Explain a physical change Explain a chemical change Recognize the evidence for each type of change. Discussion: What’s New?. Physical or chemical change? What is true about the kinds of matter present before and after a physical change?

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5.4 Physical and Chemical Changes

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  1. 5.4 Physical and Chemical Changes • Learning Goals: • Explain a physical change • Explain a chemical change • Recognize the evidence for each type of change

  2. Discussion: What’s New? Physical or chemical change? What is true about the kinds of matter present before and after a physical change? How is matter different? What substances were formed when the paper burned? What is true about the types of matter present before and after the matter undergoes a chemical change What substances were formed when the paper burned? Would it be possible to change these types of matter back into a sheet of paper?

  3. Change of Appearance Physical Changes • A physical change is a change that affects one or more physical properties of a substance. • The appearance, shape, or size of a substance may be altered during a physical change. • Physical changes, such as changes in state, do not change the chemical identity of a substance.

  4. Change of Appearance Physical Changes

  5. Change of Appearance Chemical Changes • A chemical change is the process when one or more substances change into entirely new substances with different properties. • A substance’s identity changes because the chemical makeup changes. • Bonds get rearranged and/or new bonds form. • Influenced by temperature: At higher temperatures, chemical reactions happen more quickly

  6. Change of Appearance

  7. Look for the Signs How can you tell a chemical change has happened? • There are five key signs that a chemical reaction has occurred. • Observing two or more of these signs during a change means you are likely observing a chemical change.

  8. How can you tell a chemical change has happened? • Energy that changes from one form to another can be evidence of a chemical change. -Energy can appear as a spike or drop in temperature - Energy can appear in the visible form of light.

  9. How can you tell a chemical change has happened? • Colour changes • When a substance changes to a new colour, a chemical change has likely occurred

  10. How can you tell a chemical change has happened? • Odours can be produced during a chemical change.

  11. How can you tell a chemical change has happened? • The production of gas is often evidence of a chemical change. • Fizzing and foaming may mean gases are being produced. • Boiling also can produce gas bubbles, but boiling is a physical change. Careful!

  12. How can you tell a chemical change has happened? • A precipitate is a solid formed from two clear liquids being mixed together. • The formation of a precipitate can indicate a chemical change.

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