1. IIIIIIIVV If the 4 young ladies in the front row have a combined weight of 2.15x10 11 micrograms. What is the average weight of each? Convert their weight to Pounds! World’s Most Dangerous Bellringer

2. IIIIIIIVV I.Intro to Reactions Ch. 9 – Chemical Reactions

3. A.Signs of a Chemical Reaction n Evolution of heat and light n Formation of a gas n Formation of a precipitate n Color change

4. A. Chemical Equations A+B  C+D REACTANTSPRODUCTS

5. A. Chemical Equations

6. B. Writing Equations n Identify the substances involved. n Use symbols to show: 2H 2 (g) + O 2 (g)  2H 2 O(g)  How many? - coefficient  Of what? - chemical formula  Remember the diatomic elements.  In what state? - physical state

7. B. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state? Al 2(s)(s)+ 3CuCl 2 (aq)  3 Cu(s)(s)+ 2AlCl 3 (aq)

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

9. C. Describing Equations to produce How many? Of what? In what state? Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chlorideand one molecule of hydrogen gas.

10. D. Balancing Equations n An equation is balanced when it has the same # and kind of atoms.

11. D. Balancing Equations n Law of Conservation of Mass: mass is neither created nor destroyed in a chemical reaction (Lavoisier) 4 H 2 O 4 H 2 O 4 g32 g 36 g n total mass stays the same; atoms can only rearrange.

12. D. Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3.Add coefficients to make #s equal. Coefficient  subscript = # atoms 3MgCl 2 4Ca(OH) 2 4.Reduce coefficients to lowest possible ratio, if necessary. 5.Double check atom balance!!!

13. D. Helpful Tips n Balance one element at a time. n Update ALL atom counts after adding a coefficient. n If elements appear more than once per side, balance them last. n Balance polyatomic ions as single units.  “1 SO 4 ” instead of “1 S” and “4 O”

14. Al + CuCl 2  Cu + AlCl 3 Al Cu Cl 1 1 1 1 2 3 2  3  6   3 33 2 C. Balancing Example Aluminum and copper(II) chloride form copper and aluminum chloride. 2  2  6