1. Identify the following reactions and balance them: a. C 10 H 8 + O 2  CO 2 + H 2 O b. Fe + S 8  FeS c. Pb(NO 3 ) 2 + KI  PbI 2 + KNO 3 d. Mg + H 2 O  Mg(OH) 2 + H 2

1. Identify reactants 2. Identify types of reaction. 3. To write the "correct" chemical formulas for the Products, keep these things in mind: 1. There are 7 elements that form diatomic molecules 2. Subscripts (and subscripts found outside parentheses around a polyatomic ion) are there to make the oxidation numbers in the chemical formula total zero.

 Example: MgO   Separate the compound into its two components (remember diatomic molecules) Mg and O  Oxygen forms a diatomic molecule so it will be O 2  MgO  Mg + O 2

 O 2 + Al →  Combine the elements to make a compound:  AlO  Find charges(aluminum is +3 and oxygen is − 2) and use criss cross method  O 2 + Al → Al 2 O 3

 Remember: A + BC  B + AC if A is a metal, or A + BC  AB + C if A is a nonmetal  Zn + HCl →  Zinc will switch places with the metal part of the compound.  H + ZnCl  Hydrogen forms diatomic molecules so it will be H 2  Find ionic charges (Zn is +2 and Cl is − 1) and do criss cross method.  Zn + HCl → H 2 + ZnCl 2

 Remember: AB + CD  AD + CB; AB and CD are both ionic compounds  Separate each compound & write their charges.  Switch places and re-write new compounds.  Pb(NO 3 ) 2 + KI   Reactants: Pb 2+ NO 3 - K + I -  Products: Pb 2+ I - K + NO 3 -  Pb(NO 3 ) 2 + KI  PbI 2 + KNO 3

 Can also be C x H y O z  A hydrocarbon and oxygen indicate a combustion reaction.  Just write CO 2 and H 2 O as products and then balance  C 6 H 6 + O 2 →  Products will always be CO 2 and H 2 O  C 6 H 6 + O 2  CO 2 + H 2 O

 CuCl 2 + K 2 S  What type of reaction is it?  Double-replacement  Which elements (ions) will switch places?  Copper and potassium  Which ions are present?  Cu +2 Cl -1 K +1 S -2  Use the criss cross method to form your ionic compound.  Cu +2 S -2  K +1 Cl -1  Chemical equation: CuCl 2 + K 2 S  CuS + KCl