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Balancing Equations #2
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Balancing Equations #2

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How to balance chemical equations

How to balance chemical equations

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  • 1. Balancing Equations: Chemical and Nuclear
  • 2. How molecules are symbolized
    • Cl 2 2Cl 2Cl 2
    • Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2
    • 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 O H O H Ca
  • 3. Balancing equations: MgO
    • The law of conservation of mass states that matter can neither be created or destroyed
    • Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction
    • Thus, the number of a particular atom is the same on both sides of a chemical equation
    • Example: Magnesium + Oxygen
    • Mg + O 2  MgO
    • However, this is not balanced
    • Left: Mg = 1, O = 2
    • Right: Mg = 1, O = 1
    O Mg O +  Mg O
  • 4. Balance equations by “inspection”
    • Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity.
    5 2 3 3.5 2 7 4 6 2 2 2 2 6 3 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 From Mg + O 2  MgO 2Mg + O 2  2MgO is correct Mg + ½O 2  MgO is incorrect Mg 2 + O 2  2MgO is incorrect 4Mg + 2 O 2  4MgO is incorrect
  • 5.
    • a) Mg + 2 HCl  MgCl 2 + H 2
    • b) 3 Ca + N 2  Ca 3 N 2
    • c) NH 4 NO 3  N 2 O + 2 H 2 O
    • d) 2 BiCl 3 + 3 H 2 S  Bi 2 S 3 + 6 HCl
    • e) 2 C 4 H 10 + 13 O 2  8 CO 2 + 10 H 2 O
    • f) 6 O 2 + C 6 H 12 O 6  6 CO 2 + 6 H 2 O
    • g) 3 NO 2 + H 2 O  2 HNO 3 + NO
    • h) Cr 2 (SO 4 ) 3 + 6 NaOH  2 Cr(OH) 3 + 3 Na 2 SO 4
    • i) Al 4 C 3 + 12 H 2 O  3 CH 4 + 4 Al(OH) 3
    skeleton(UNBALANCED) equations:
  • 6.
    • 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 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  3 3 3 2 2 3 2 ½ 2 2 2 3 2 4 Cu Hg Ag Ca Mg Al Zn Fe Ni Sn Pb H Au Li Na K
  • 7.
    • a) 2 KNO 3  2 KNO 2 + O 2
    • b) 2 Pb(NO 3 ) 2  2 PbO + 4 NO 2 + O 2
    • c) P 4 + 6 I 2  4 PI 3
    • d) 3 MgO + 2 H 3 PO 4  Mg 3 (PO 4 ) 2 + 3 H 2 O
    • e) Br 2 + 2 KI  I 2 + 2 KBr
    • f) Ca(OH) 2 + 2 HNO 3  Ca(NO 3 ) 2 + 2 H 2 O
    • g) Bi 2 O 3 + 3 H 2  2 Bi + 3 H 2 O
    • h) 3 Fe + 2 O 2  Fe 3 O 4
    • i) 2 CaO + 5 C  2 CaC 2 + CO 2
    Here are some more to balance: