CHEMICAL EQUATIONS

1
CHEMICAL EQUATIONS

• LAW OF CONSERVATION OF MASS
• BALANCING FOR CONSERVATION OF MASS
• TYPES OF CHEMICAL REACTIONS

2
Levoisier And Balancing

• Levoisier summarizied his observations of
  chemical change by stating, among other things,
  that during a chemical change matter is
  conserved.
• That is, matter is neither created or destroyed.
• The mass of the reactants equals the mass of the
  products.

3
Comprehension

• A balanced equation has the same number of
  atoms of each element in both the reactant and
  product sides of the equation.
• Reactants Products
• C O2 CO2
• Two elements make a compound (addition )
• Balance
• (1) carbon atom (1) carbon atom
• (2) oxygen atoms (2) oxygen atoms

4
Consolidation

• Reactants Products
• 2H2O 2H2 O2
• a compound makes Two elements
  (decomposition )
• Balance
• (4) hydrogen atoms (4) hydrogen atoms
• (2) oxygen atoms (2) oxygen atoms

5
A Three Step Approach

• First a word equation is written to summarize the
  reaction in words.
• hydrogen oxygen water
• The above is read as Hydrogen gas molecules
  react with oxygen gas molecules to produce water
  molecules
• Then a skeleton equation is written with all the
  correct formulas for the substances.
• H2(g) O2 (g) H2O(l)
• Then the equation is balanced for conservation of
  mass. (Large multipliers are placed in front of
  substances to balance the equation)
• 2H2 O2 2H2O

6
Mechanics of Balancing

• Where do you start?
• To start avoid elements which occur more than
  once on a side. Start with those occurring only
  once on a side
• Pb in PbO2 HBr-gt H2O PbBr2 Br2
• Balance complex ions as units rather than
  individual elements whenever possible.
• e.g. NO3, SO4
• Al2(SO4)3 3Ba(NO3)2-gt2Al(NO3)3 3BaSO4
• Avoid elements which occur by themselves until
  last.
• Be methodical. Dont jump around balancing a bit
  here and there.

7
Types of Chemical Reactions

• Reactants Products
• C O2 CO2 (addition )
• two elements make a compound
• 2 H2O 2 H2 O2 (decomposition)
• a compound make two elements
• AgNO3 Cu Cu NO3 Ag (single replacement)
• compound reacts with element to as metal ions
  switched places
• AgNO3 Cu SO4 Cu NO3 Ag SO4 (double
  replacement)
• compound reacts with compound as metal ions
  switch places
• CH4 2O2 CO2 2H2O (hydrocarbon
  combustion)
• hydrocarbon reacts with oxygen to make
  carbon dioxide and water

8
Conclusions

• The types of chemical reactions can be used to
  predict possible products given the reactants.
• The reaction is then done and the products are
  observed to verify the prediction.
• What evidence would you expect to verify in the
  following?
• AgNO3 Cu Cu NO3 Ag (replacement)
• __HCl Mg MgCl2 H2 (replacement)
• Complete this skeleton equation
• CuSO4 Fe