PowerPoint Presentation

							Chemical Equations


      Chemistry
      Mrs. Coyle
Chemical Equations:
        represent chemical reactions

 Word Equations
 Skeleton Chemical Equations
 Balanced Chemical Equations
    Word Equations: show the names of
    the reactants and the products

 Reactants             Products

Methane + Oxygen  Carbon Dioxide + Water

 The arrow (yield sign) and indicates that a
 reaction took place.
Skeleton Chemical Equations
 The formulas of the reactants and
 products are written without indicating
 their relative amounts.

Example:
           CH4+ O2 CO2 +H2O
 Balanced Chemical Equations
 The chemical formulas and the relative
  amounts of the reactants and products are
  written.
Example:
      CH4 + 2O2 CO2 + 2H2O

 The coefficients indicate the relative amounts
  of each substance.
 Equal number of atoms of each element must
  appear on both sides of the balanced equation.
Why does a chemical reaction have to
be balanced?
 In any chemical or physical
 change, mass is neither created or
 destroyed

 Mass is CONSTANT

 Law of Conservation of Mass
 (Antoine Lavoisier)
Combustion of Methane
CH4 + 2O2 CO2 +             2H2O




     Atoms are rearranged!
 Example: Decomposition of hydrogen
 peroxide in the presence of a catalyst.
 Word equation:


hydrogen peroxide  water + oxygen
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
 Skeleton equation:


H 2O 2           H 2O   +   O2
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
 Balanced Equation:


2H2O2                 2H2O   +   O2
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
Balanced equation showing
 the catalyst (MnO2)
 the state of the reactants and products:


                 MnO2
2H2O2(l)                2H2O (l)    +       O2 (g)