BACK                                           Chemical Reactions and Equations

I  The nature of Chemical Reactions
    A. chemical reactions
        1.  chemical reaction: a process in which one or more substances are converted
             into new substances with different physical and chemical properties
        2.  two parts
              a.  reactants:  substances that enter into a reaction
              b.  products:  substances produced by a reaction
    B.  the reason for reactions
        1.  to obtain a complete set of valence electrons
        2.  to become more stable

II  Chemical Equations
    A.  represents a chemical reaction
    B.  word equations
        1.  simplest type
        2.  give names of the reactants and products
        3.  methane + oxygen ---> carbon dioxide + water
        4. + means reacts
        5.  ---> means yields or produces
        6.  direction of arrow points to the products
    C.  formula equation
        1.  uses chemical symbols and formulas
        2.  CH4 + O2 ---> CO2 + H2O
    D.  balancing chemical equation
        1.  the number of atom of each element must be the same before and after the reaction
        2.   CH4 + O2 ---> CO2 + H2O
                       1C        ---> 1C
                      4 H       ---> 2 H     equation is not balanced
                      2 O       ---> 3
        3.  can not change the subscripts in the formulas - would change the substance identity
        4. must use coefficients written before the formulas of the reactants and products
        5.  CH4 + 2O2 ---> CO2 + 2H2O
                       1C         --->   1C
                       4 H        ---> 4 H  equation is balanced
                       4 O        ---> 4 O
    E.  writing complete chemical equations
        1.  equation include the physical state of the reactants and products
        2.  (s)     - solid
             (g)     - gas
             (l)      - liquid
             (aq)   - aqueous: solid dissolved in water
        3.  CH4 (g) + 2O2 (g) ---> CO2 (g) + 2H2O (g)


III  Classifying Chemical Reactions
    A.  4 general types
        1.  direct combination (composition or synthesis)
              a.  two or more reactants form a single product
              b.  A+B-->AB   general form
              c.  S+O2--> SO2
                  CO2 + H2O --> H2CO3
        2.  decomposition reactions
              a.  single compound is broken down into two or more simpler substances
              b.  AB --> A+B    general form
              c.  CaCO3 --> CaO + CO2
        3. single-replacement reactions
              a.  an element replaces an element in a compound
              b.  reactants are an element + compound
              c.  A + BX --> AX + B
              d.  Fe + CuSO4 --> FeSO4 + Cu
              e.  requirement:  the replacing element must be more chemically active than the element being replaced
              f.  active series - list of elements from the most active on the top decreasing as you move down the list to the least active on the bottom
              g.  a higher listed element can replace a lower listed element - the reverse can not occur
        4.  double-replacement reactions
              a.  two ionic compounds are reactants and two compounds are products
              b.  an atom or ion from each compound replace each other
              c.  AX + BY --> AY + BX    general form
              d.  CaCO3 + HCl --> CaCl2 + H2CO3
              e.  requirement:  one product must be
                  1.  molecular compound
                  2.  precipitate
                  3.  gas

    B.  some exceptions to the rule
        1.  some reaction do not fit into any of the 4 types
        2. combustion reaction - CH4 + 2O2 ---> CO2 + 2H2O





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