Activity #28- Signs of a Chemical Reaction

Chemical Reactions Occur when new substances are formed by changing the way in which atoms are arranged. REACTANTS= substances used in a chemical reaction PRODUCTS= substances formed by chemical reaction

Atoms in a Chemical Reaction

6 Signs of a Chemical Reaction Color Change Formation of a Gas Endothermic Reaction Exothermic Reaction Formation of a Precipitate Odor Change

Sign #1: Color Change Reactants: Cabbage Juice and Vinegar; Cabbage Juice and Baking Soda Add 10 mL of cabbage juice to 2 test tubes Add 3 drops of vinegar to one test tube Add one lab scoop of baking soda to another

6 Signs of a Chemical Reaction! COLOR CHANGE Substances change color Color change is a product of two or more reactants Examples: Rust, leaves changing color, mold

Sign #2: Formation of a Gas Reactants: Baking Soda and Vinegar (Acetic Acid) 10 mL of Vinegar in test tube 1 lab scoop of baking soda

6 Signs of a Chemical Reaction! FORMATION OF A GAS Bubbles often appear Fizzes A product gas is leaving the reaction mixture Examples: vinegar + baking soda = carbon dioxide

Sign #3: Endothermic Reaction Reactants: Citric Acid and Baking Soda 10 mL Citric acid in test tube Take temperature Combine w/ 1 lab scoop of baking soda Swirl and observe temperature!

6 Signs of a Chemical Reaction! ENDOTHERMIC REACTION (temperature/energy change) Chemical bonds break Energy (heat) is absorbed from surroundings Substance seems cooler Examples: baking, cold packs, photosynthesis

Sign #4: Exothermic Reaction Reactants: Hydrogen Peroxide and Yeast 10 mL Hydrogen Peroxide in test tube Take temperature Combine w/ 1 lab scoop of yeast Swirl and observe temperature!

6 Signs of a Chemical Reaction! EXOTHERMIC REACTION (temperature/energy change) Chemical bonds are made Energy (heat) is released to surroundings Substance seems warmer Examples: fireworks, explosions, hand warmers

Sign #5: Formation of a Precipitate Reactants: Ammonia and dissolved Epsom Salt

6 Signs of a Chemical Reaction! A PRECIPITATE IS FORMED A solid that forms when two liquids combine The solid particles are the product Examples: Kidney stones, pearls, cheese

6 Signs of a Chemical Reaction! 6. ODOR CHANGE Produces new smells as the reaction occurs Examples: Rotting, bad breath, body odor