3. How molecules are symbolized Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca Notice that the OH is a group The 2 refers to both H and O How many of each atom are in the following? a) NaOH b) Ca(OH) 2 c) 3Ca(OH) 2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6 Cl 2 2Cl 2Cl 2

4. Balancing equations: MgO Dalton: chemical reactions are the result of a rearrangement of atoms. Lavoisier: Conservation of Mass – “What goes in must come out” Number and types of atoms must be conserved. Thus, the number of a particular atom is the same on both sides of a chemical equation Example: Magnesium + Oxygen Mg + O 2  MgO O MgO +  O However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1

5. Representing Reactions Word Equation: Magnesium + hydrochloric acid  magnesium chloride + hydrogen Skeleton Equation: Mg (s) + HCl (aq)  H 2 (g) + MgCl 2 (aq) When going from word equations to skeleton equations, don’t forget about HOBrFINCl gases!

6. 1.Balance the element with the greatest number of atoms (not H or O!) 2.Balance other elements in compounds. If an element is uncombined, usually leave it until last. 3.Balance H or O, if they are combined in compounds 4.Balance uncombined elements 5.Check Balancing Equation Guidelines:

7. 5 233.5 2746 222 263 C 2 H 6 + O 2  CO 2 + H 2 O a)P 4 + O 2  P 4 O 10 b)Li + H 2 O  H 2 + LiOH c)Bi(NO 3 ) 3 + K 2 S  Bi 2 S 3 + KNO 3 d)C 2 H 6 + O 2  CO 2 + H 2 O

8. a)Mg + HCl  MgCl 2 + H 2 b)Ca + N 2  Ca 3 N 2 c)NH 4 NO 3  N 2 O + H 2 O d)BiCl 3 + H 2 S  Bi 2 S 3 + HCl e)C 4 H 10 + O 2  CO 2 + H 2 O f)O 2 + C 6 H 12 O 6  CO 2 + H 2 O g)NO 2 + H 2 O  HNO 3 + NO h)Cr 2 (SO 4 ) 3 + NaOH  Cr(OH) 3 + Na 2 SO 4 i)Al 4 C 3 + H 2 O  CH 4 + Al(OH) 3 Balance these skeleton equations:

9. a)Mg + 2HCl  MgCl 2 + H 2 b)3Ca + N 2  Ca 3 N 2 c)NH 4 NO 3  N 2 O + 2H 2 O d)2BiCl 3 + 3H 2 S  Bi 2 S 3 + 6HCl e)2C 4 H 10 + 13O 2  8CO 2 + 10H 2 O f)6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O g)3NO 2 + H 2 O  2HNO 3 + NO h)Cr 2 (SO 4 ) 3 + 6NaOH  2Cr(OH) 3 + 3Na 2 SO 4 i)Al 4 C 3 + 12H 2 O  3CH 4 + 4Al(OH) 3 Balance these skeleton equations:

10. We have looked at several types of reactions without worrying about balancing However, all equations should be balanced Predict the products and balance these: (recall, metals above replace metals below, reactions with water yield metal hydroxides) Cu + Fe 2 (SO 4 ) 3 NR (no reaction) Zn + Li 2 CO 3 Cu + AlCl 3 K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au Returning to reaction types Fe + CuSO 4  LiOH + H 2 Al 2 O 3 2 Ni+ NaCl  Al+ CuCl 2  Li+ ZnCO 3  Li + H 2 O  Al+O 2  33 3223 2 ½222 324

11. a)KNO 3  b)Pb(NO 3 ) 2  c)P 4 + I 2  d)MgO + H 3 PO 4  e)Br 2 + KI  f)Ca(OH) 2 + HNO 3  g) Bi 2 O 3 + H 2  h)Fe + O 2  i)CaO + C  Here are some more to complete & balance:

12. a)2KNO 3  2KNO 2 + O 2 b)2Pb(NO 3 ) 2  2PbO + 4NO 2 + O 2 c)P 4 + 6I 2  4PI 3 d)3MgO + 2H 3 PO 4  Mg 3 (PO 4 ) 2 + 3H 2 O e)Br 2 + 2KI  I 2 + 2KBr f)Ca(OH) 2 + 2HNO 3  Ca(NO 3 ) 2 + 2H 2 O g) Bi 2 O 3 + 3H 2  2Bi + 3H 2 O h)3Fe + 2O 2  Fe 3 O 4 i)2CaO + 5C  2CaC 2 + CO 2 Here are some more to balance: