Chemical Equations

1
Section 3.1

• Chemical Equations

2
ReviewElement Symbols

• All elements are represented by a 1 or 2 letter
  symbol
• For example
• C Carbon
• Ne Neon
• O Oxygen
• The symbols are shown on the periodic table

3
ReviewChemical Formulas

• Shows the elements number of atoms of each
  element in a molecule
• H2SO4
• Elements
• Hydrogen 2 atoms
• Sulfur 1 atom
• Oxygen 4 atoms
• 7 atoms total

Subscript
4
Coefficients

• A formula may begin with a number.
• If there is no number, then 1 is understood to
  be in front of the formula.
• This number is called the coefficient.
• The coefficient represents the number of
  molecules of that compound or atom needed in the
  reaction.
• For example
• 2H2SO4 2 molecules of Sulfuric Acid

5
Coefficients

• 2H2SO4 2 molecules of Sulfuric Acid
• A coefficient is distributed to ALL elements in a
  compound
• 2 H2 (for a total of 4 H atoms)
• 2 S (for a total of 2 S atoms)
• 2 O4 (for a total of 8 O atoms)

6
Chemical Equations

• A chemical equation is written as an expression
  similar to a mathematic equation that can be
  compared to a recipe that a chemist follows in
  order to produce desired results.

7
Chemical Equations

• All chemical equations have reactants and
  products.
• We express a chemical equation as follows
• Reactants ? Products
• The arrow is equivalent to an math. When we
  describe the equation we use the word yields or
  produces instead of equals

8
Equation Example
The burning of methane gas in oxygen is CH4
2 O2 ? CO2 2 H2O
9
Conservation of matter

• The law of conservation of matter tells us that
  matter can neither be created nor destroyed. It
  is transformed from one form to another.
• We follow the conservation of matter law when we
  balance equations.

10
Balancing a Chemical Equation

• A chemical equation is balanced when the ions or
  atoms found on the reactant side of the equation
  equals that found on the product side.
• The arrow can be considered the balance point.

11
Coefficients

• We use coefficients in front of elements or
  compounds on either side of the reaction to
  balance the equation. (The coefficients go in
  front of the chemical!)
• We cannot change subscripts because it would
  create new materials that are not part of
  reaction process.

12
Balance this equation!

• Na Cl2 NaCl
• Na- 1 Na-1
• Cl- 2 Cl-1
• note that the number of sodium balances but the
  chlorine does not. We will have to use
  coefficients in order to balance this equation.

13
Inserting subscripts

• Na Cl2 2 NaCl
• Na- 1 Na-1 2
• Cl- 2 Cl-1 2
• Now the chlorine balances but the sodium does
  not! So we go back and balance the sodium.

14
Finally balanced!

• 2Na Cl2 2 NaCl
• Na- 1 2 Na-1 2
• Cl- 2 Cl-1 2
• Since the number of each element on the
  reactant side and the product side of the
  equation are equal, the equation is balanced.

15
Balancing Equation Practice

• CuCl3 Li2S ? Cu2S3 LiCl
• NiNO3 KCl ? NiCl KNO3
• FeCl3 Na2O ? Fe2O3 NaCl

16
Answers

• 1. 2CuCl3 3Li2S ? Cu2S3 6LiCl
• 2. NiNO3 KCl ? NiCl KNO3
• (already balanced)
• 3. 2FeCl3 3Na2O ? Fe2O3 6NaCl

17
Section 3.2

• Simple Patterns of Chemical Reactivity

18
Identifying Reaction Types

• Reactions are classified by their products.
• There are several different types of chemical
  reactions. The 5 basic types of chemical
  reactions we will study are synthesis or
  combination reactions, decomposition reactions,
  single replacement reactions, double replacement
  reactions, and combustion reactions.

19
Combination or Synthesis reactions

• Synthesis (meaning to make) or combination
  reactions are typified by their single product.
• If you have a reaction in which at least 2
  elements or compounds are reacted and produce a
  single product, the reaction is a synthesis
  reaction.

20
Synthesis Reactions

• A B ? AB
• Note Single Product! This is your clue that
  this is a synthesis or combination reaction.

21
Decomposition Reactions

• Decomposition reactions are really just the
  opposite of a synthesis reaction. Remember, if
  you can make a substance, you should be able to
  break it back apart into its components.
• A good way to remember decomposition reactions to
  to remember what happens when something
  decomposes. It falls apart!

22
Decomposition Reactions

• AB ? A B
• Note Single Reactant! The single reactant is
  your clue that this is a decomposition reaction.
  

23
Single Replacement Reactions

• Single replacement reactions occur when one
  chemical takes the place of another in a
  reaction.
• In the typical single replacement reaction, an
  element trades places with one of the ions in a
  compound.

24
Single Replacement Reactions

• A CD ? AD C
• Note Element A replaces ion C in the reaction.
  The clue in this reaction is
• ElementCompound ? Element Compound

25
Double Replacement Reactions

• Double replacement reactions are identified by
  two ions trading places and forming new
  compounds.

26
Double Replacement Reactions

• AB CD ? AD CB
• Note Notice that one ion from compound AB
  replaces one ion from compound CD.
• Clue
• CompoundCompound?CompoundCompound

27
Combustion Reactions

• Combustion reactions are the ones that burn (or
  explode!).
• Most involve O2 as a reactant
• These reactions are identified by their products.
  They either produce carbon dioxide and water.
• Hydrocarbons compounds are very combustible.

28
Combustion Reactions

• CH4 O2 ? CO2 H2O
• They may also be written
• CH4 ? CO2 H2O
• (O2 is usually written above the arrow.)
• Clue CO2 (carbon dioxide) in the product along
  with water