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Science Dept.

Chemistry CHE 100 Notes
I. Chemical Equations

1. Chemical "Shorthand"
   1. Reactants are written on the Left

   2. Products are written on the Right

   3. Arrows show the direction of the reaction ---> or <--- or <===>;
      forward and backward arrows denote a reversible reaction

   4. Plus sign + on the line means AND

   5. H_2(g); the subscript _(g) denotes a gas

   6. H₂O_(l); the subscript _(l) denotes a liquid

   7. NaCl_(s); the subscript _(s) denotes a solid

   8. AgCl_(ppt); the subscript _(ppt) denotes a solid precipitate

   9. If a substance is underlined, it denotes a chemical precipitate

   10. A downward arrow written next to a substance denotes a chemical precipitate

   11. An upward arrow written next to a substance denotes an escaping gas

   12. NaCl_(aq); the subscript _(aq) denotes an aqueous or water solution

   13. --^Pt--> denotes the use of a catalyst, in this case Platinum

   14. --^{^}--> or >--^heat--> denotes the use of activation Energy

   15. Remember, because of the Law of Conservation of Mass,
       equations must be balanced

2. Guidelines For Balancing Chemical Equations
   1. Guidelines
      1. Write correct formulas for the reactants and the products, and use the correct signs

      2. Choose the compound that has the greatest number of atoms of an element and then balance both sides of the equation

      3. Balance the polyatomic ions that do not change

      4. Balance the H and the O atoms

      5. Check all coefficients - all have to be whole numbers and the lowest ratio

      6. Check the balance from Left to Right

   2. Some Questions
      1. Does a Reaction Go?
         1. In the Equation to Predict
            1. Use the Solubility Table
            2. Use the Electromotive Series
            3. Use Previous Experience with Similar Reactions

         2. In the Experiment
            1. Gas Given Off ... Fizzing
            2. Foaming
            3. Color Change
            4. Light Given Off
            5. Heat Given Off
            6. Explosion
            7. Formation of a Precipitate

      2. If It Goes, How Fast Does It Go?

      3. Is there any Oxidation - Reduction?
         1. Oxidation - Loss of Electrons and an Increase in Oxidation Number

         2. Reduction - Gain of Electrons and a Decrease in Oxidation Number

3. Some Examples to Balance
   1. Fe_(s) + _____ HCl_(aq) ----> FeCl_2(aq) + H_2(g)

   2. _____Ca(OH)_2(aq) + _____H₃PO_4(aq) ----> Ca₃(PO₄)_2(aq) + _____ H₂O_(l)

   3. CH_4(g) + _____ O_2(g) ----> CO_2(g) + _____ H₂O_(l)

4. Types of Chemical Reactions
   1. Combination or Synthesis Reactions

   2. Decomposition Reactions

   3. Single Replacement (or Displacement) Reactions

   4. Double Replacement (or Displacement) Reactions, Also Known as Metathesis

   5. Neutralization Reactions

5. Combination or Synthesis Reactions
   1. A + Z ----> AZ

   2. _____ Fe_(s) + _____ O_2(g) ----> _____ Fe₂O_3(s)

   3. _____ Na_(s) + Cl_2(g) ----> _____ NaCl_(s)

   4. S_(s) + O_2(g) ----> SO_2(g)

   5. H₂O_(l) + SO_3(g) ----> H₂SO_4(aq)

   6. _____ Mg_(s) + O_2(g) ----> _____MgO_(s)

   7. H₂O_(l) + MgO_(s) ----> Mg(OH)_2(aq)

6. Decomposition Reactions
   1. AZ ----> A + Z

   2. 2HgO_(s) ----> 2Hg_(l) + O_2(g)

   3. CaCO_3(s) --^heat--> CaO_(s) + CO_2(g)

   4. 2H₂O_(g) --^DC--> 2H_2(g) + O_2(g)

7. Single Replacement (or Displacement) Reactions
   1. A + BZ ----> AZ + B or X + BZ ----> BX + Z

   2. Does a Reaction Go? Use the Electromotive Series:
      For metals, any element on the Left can replace any element on the Right in solution.

      Li K Ba Ca Na Mg Al Zn Fe Cd Ni Sn Pb (H) Cu Hg Ag Au

   3. For nonmetals, any element on the Left can replace any element on the Right in solution.

      F Cl Br I

   4. Fe_(s) + CuSO_4(aq) ----> FeSO_4(aq) + Cu_(s)

   5. Zn_(s) + H₂SO_4(aq) ----> ZnSO_4(aq) + H_2(g)

   6. Zn_(s) + 2AgNO_3(aq) ----> Zn(NO₃)_2(aq) + 2Ag_(s)

   7. Cl_2(g) + 2NaBr_(ag) ----> 2NaCl_(aq) + Br₂

8. Double Replacement (or Displacement) Reactions, Also Known as Metathesis
   1. AX + BZ ----> AZ + BX

   2. Does a Reaction Go? Use Information on Solubility

   3. AgNO_3(aq) + HCl_(aq) ---> HNO_3(aq) + AgCl_(ppt)

   4. CaCO_3(s) + 2HCL_(aq) ----> CaCl_2(aq) + H₂O_(l) + CO_2(g)

9. Neutralization Reactions
   1. HX + BOH ----> BX + HOH

   2. HCl_(aq) + NaOH_(aq) ---> NaCl_(aq) + HOH_(l)

   3. H₂SO_4(aq) + Ba(OH)_2(aq) ----> BaSO_4(aq) + 2H₂O_(l)

10. Definitions
    1. Exothermic:

    2. Endothermic:

11. How About a Quick Quiz?