1. Chemical Reactions

2. A change in which one or more substances are converted to different substances. A+B  C+D REACTANTSPRODUCTS

3. Law of Conservation of Mass In a chemical reaction, matter is not created or destroyed. Atoms can only rearrange. Discovered by Lavoisier. 4H 2O 4H 2O

4. Chemical Equations Aqueous lead(II) nitrate plus two units of aqueous potassium iodide produces solid lead(II) iodide and two units of aqueous potassium nitrate. Pb(NO 3 ) 2 (aq)+2KI(aq)  PbI 2 (s)+2KNO 3 (aq) Coefficient - # of units of each substance

5. Chemical Equations Describing Coefficients: individual atom = “atom” 2Mg  2 atoms of magnesium covalent substance = “molecule” 3CO 2  3 molecules of carbon dioxide ionic substance = “unit” 4MgO  4 units of magnesium oxide

6. Chemical Equations

7. Metals and the Atmosphere When iron is exposed to air and moisture, it corrodes or rusts, forming hydrated iron (III) oxide. Rust can seriously damage iron structures because it crumbles and exposes more iron to the air.

8. Metals and the Atmosphere Aluminum also reacts with oxygen in the air to form aluminum oxide. Unlike rust, aluminum oxide adheres to the aluminum surface, forming an extremely thin layer that protects the aluminum from further attack.

9. Metals and the Atmosphere Copper is another metal that corrodes when it is exposed to air, forming a blue-green coating called a patina. You can see this type of corrosion on many public monuments.