1. Forming New Substances Chapter 2 Section 1 p. 28 -31 Vocabulary 1. chemical reaction 2. precipitate

2. 1. Chemical reaction A process in which one or more substances change to make one or more new substances. The chemical and physical properties of the new substances are completely different from the original substances that make them up. =

3. 2. precipitate – a solid substance that is formed as the result of a chemical reaction in a solution.

4. Signs of a Chemical Reaction p. 28

5. ALWAYS… 1. A new substance with new properties is formed. *************************************************************** Usually, but not always… 2. Bubbling or fizzing – gas forms – change in odor 3. Color change 4. Heat given off 5. Light given off 6. Sound given off 7. It is not easily reversible 8. A precipitate forms

6. Bonds: Holding Molecules Together p. 30 A chemical bond is a force that holds two atoms together in a molecule. For a chemical reaction to take place, the original bonds must break and new bonds must form. Molecules are always moving. If the molecules bump into each other with enough energy, the chemical bonds in the molecules break. The atoms then rearrange, and new bonds form to make new substances

7. Quiz Time! 1. What is a precipitate? A precipitate is a solid that has formed as the result of a chemical change in a solution. 2. Name four possible signs that a chemical change has taken place. gas forms (bubbles, fizz, odor), precipitate forms, color change, heat, light, or sound given off, not easily reversible, new substance with new properties forms. 3. What is the number one sign that a chemical change has taken place? A new substance with new properties is formed. 4. What happens to chemical bonds during a chemical reaction? They break and new ones are formed.

8. 5. Most chemical reactions: A. have starting substances that collide with each other. B. do not break bonds. C. do not rearrange atoms. D. cannot be seen A. 6. What evidence of a chemical reaction is shown in the picture? New substance with new properties has formed, color change, heat given off, sound given off, new odor, not easily reversible 8. Steam is escaping from a teapot. Is this a chemical reaction? Explain. Physical change, steam is just another form of water. 7. What is happening to the bonds of the starting substance in the picture? The bonds are being broken and the atoms are rearranged to create a new substance.