Classifying Chemical Reactions

1
Classifying Chemical Reactions

• Section 24.3

2
Classifying Reactions

• Classify reactions in order to predict products
• Five main types synthesis, combustion,
  decomposition, single displacement, and double
  displacement
• Synthesis reaction - two or more substances
  combine to form another substance.
• For example A B ? AB
• 2H2 O2 ? 2H2O
• 2 or more simpler substances ? one more complex
  substance

3
Predicting Synthesis Products

• When forming a compound, be sure to pay attention
  to
• Covalent- the Lewis dot structure must be correct
• Ionic- you must get the correct charges and use
  the crisscross method appropriately

4
Classifying Reactions

• Decomposition - opposite of synthesis.
• One substance breaks down into 2 or more other
  substances.
• AB ? A B
• One compound? 2 or more simpler substances
• 2H2O ? 2H2 O2
• Make sure that you pay attention to diatomics
• Make sure that you change ionic compounds into
  the pure substances.

5
Classifying Reactions

• Single displacement reaction- one element
  replaces another element in a compound
• A BC ? AC B
• Element compound ? new element new compound
• Zn CuSO4 ? ZnSO4 Cu
• Activity series- a list of metals from most to
  least active-allows us to predict which metal
  will replace which other metal.
• The more active solid metal will replace the less
  active aqueous metal

6
Single Displacement Reactions

• How to I write my new formulas?
• First use the activity series to see if a new
  substance is formed or not
• Separate the aqueous compound into its ions
• Make the solid metal into an ion.
• Combine the new metal ion with the old anion-
  remember to use the crisscross method
• Write it on the product side. It will be aqueous
• Make the old metal cation into a solid metal on
  the product side

7
Classifying Reactions

• Double displacement- positive ion of one compound
  replaces the positive ion of the other
• AB CD ? AD CB
• 2 compounds ?2 new compounds
• Forms precipitate, covalent compound, or gas
  usually
• Precipitate- Insoluble compound formed from two
  solutions that experience a double displacement
  reaction

8
Double Displacement Reactions

• How do I figure out the identity of the new
  compounds?
• 1) Separate your aqueous (aq) substances into
  their ions.
• 2) Switch the places of the cations. (bond them
  to the anion they werent bonded to before)
• 3) Follow your rules for writing formulas to do
  this correctly- remember the crisscross method
• 4) Now look at the two possible substances on
  your solubility chart to see which is the
  precipitate
• a) The precipitate will have an I or an
  sS beside it to indicate that it is insoluble
  or slightly soluble.
• b) If it has an S beside it, it is
  soluble and will not form a precipitate

9
Combustion

• Combustion- reaction of a substance with oxygen
• Often produces heat and light
• If it is combustion of a hydrocarbon, you always
  get CO2 and H2O (both gases)
• Oxygen (O2) is always a reactant.