 Law of Conservation of Matter:  Matter cannot be created or destroyed.  AMOUNT OF REACTANTS = AMOUNT OF PRODUCTS ! ! ! !

 Guidelines for Balancing Chemical Equations:  1) Do NOT change the subscripts !  2) Every element MUST have the same amount of atoms on both sides of the equation.  3) To balance, stoichiometric coefficients (numbers) are added in front of the chemical formula until we have the same atom amount on both sides of the equation.

  4) Once a coefficient is added, go back and check the rest of the equation.  5) Balance every element EXCEPT Hs and Os. Then balance Hs, Os last. Balance hydrogens with an even number  6) CHECK EQUATION TO BE SURE EVERYTHING BALANCES/CANCELS OUT ON BOTH SIDES ! ! ! Guidelines (cont.)

  Elements found in only ONE compound on each side—balance first  Polyatomic ions usually stay together—balance as a unit.  Elements in diatomic state? Balance compounds with these elements using an EVEN number  Do not be afraid to use FRACTIONS as coefficients !!  Sometimes the easiest way to balance  Use common multiplier and multiply all coefficients to get rid of the fraction Helpful Hints

 Example 1: KI (aq) + Pb(NO 3 ) 2  KNO 3 + PbI 2

 Example 2: C 2 H 6 + O 2  CO 2 + H 2 O

 Practice  1) Zn + CrCl 3  CrCl 2 + ZnCl 2  2) Cu + H 2 SO 4  CuSO 4 + SO 2 + H 2 O  3) FeI 3 + K 2 SO 4  KI + Fe 2 (SO 4 ) 3  4) CaSO 4 + Al(NO 3 ) 3  Ca(NO 3 ) 2 + Al 2 (SO 4 ) 3

 Telling a story….

 Writing Chemical Equations 1)Identify reactants, write chemical formulas. 1)Identify products, write chemical formulas. 3) Write the complete chemical equation. 4) Balance the equation.

 Example 1: Copper (II) carbonate  copper (II) oxide + carbon dioxide

 Example 2:  Merry and Pippin find lead (II) chloride and lithium sulfate in Gandalf’s chemical supply cabinet. They combine these chemical compounds and then run to Gandalf so he may identify the produced chemical compounds. Gandalf identifies the compounds as lead (II) sulfate and lithium chloride.

 Diatomic elements  Bromine (Br 2 )  Chlorine (Cl 2 )  Fluorine (F 2 )  Hydrogen (H 2 )  Iodine (I 2 )  Nitrogen (N 2 )  Oxygen (O 2 )

 Example 3:  A chemist at a Wake Forest chemistry lab prepares a potassium bromide solution dissolved in water to react with chlorine gas. This reaction produces bromine in the liquid state and potassium chloride in solution.

  Merry and Pippin have gotten in over their heads AGAIN!! Without Gandalf, they have combined a liquid phosphorus-chlorine compound which is 77.45% Cl by mass with water. Gandalf hears the commotion and immediately returns to identify an aqueous solution of phosphoric acid and hydrochloric acid. Example 4:

 1)Ariel swam down to her treasure trove to collect silver iodide and iron (III) carbonate, which she transformed into iron (III) iodide and silver carbonate for Cinderella’s birthday. 2) Cinderella decided to combine some leftover zinc sulfate and lithium carbonate in her mop bucket. After some bibbidi-bobbidi-boo; she discovers she has made zinc carbonate and lithium sulfate. Practice

  Read pp  Problems p. 118 #53-57 Homework