1. How Can You Tell When a Chemical Reaction has Happened?

2. I. Signs of a chemical reaction
Formation of a gas
1. Look for bubbles
2. Example: baking soda and vinegar produce carbon dioxide

3. B. Change of color Example 1
B. Change of color Example 1. Iron changes color when it rusts and turns to ferrous oxide 2. Bromothymal blue changes color when mixed with an acid

4. C. Change of odor Examples 1
C. Change of odor Examples 1. Milk changes its smell when it goes sour 2. The smell of onions changes when you cook them

5. D. Production of a precipitate 1
D. Production of a precipitate 1. precipitate means a solid that forms and falls to the bottom 2. Example: Cadmium Nitrate, Cd(NO3)2 poured into Sodium Sulfide, Na2S produces a bright orange precipitate of Cadmium Sulfide, CdS.

6. E. Change in energy Examples 1. Hand warmers: exothermic 2
E. Change in energy Examples 1. Hand warmers: exothermic 2. Cold pack: endothermic F. Chemical reaction should have 2 or more of these signs