Classifying Chemical Reactions

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Chapter 9

• Classifying Chemical Reactions

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Types of Reactions

• We will consider five types of reactions
• Single displacement reactions
• Double displacement reactions
• Decomposition reactions
• Synthesis reactions
• Combustion reactions

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1. Single Replacement Reactions

• Single Replacement Reactions occur when one
  element replaces another in a compound.
• A metal can replace a metal () OR a nonmetal
  can replace a nonmetal (-).
• element compound? compound element
• A BC ? AC B (if A is a metal) OR
• A BC ? BA C (if A is a nonmetal)
• (remember the cation always goes first!)
• In a single replacement reaction it is better to
  write H2O as HOH because it will split into H
  and OH- (not H and O2- !!)

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Single Replacement

• A small piece of lithium metal is added to water.

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Single Replacement Reaction
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Single Replacement Reactions

• Sodium chloride solid reacts with fluorine gas
• NaCl(s) F2(g) ? NaF(s) Cl2(g)
• unbalanced

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Single Replacement Reactions

• Zinc metal reacts with aqueous nickel (II)
  nitrate
• Zn(s) Ni(NO3)2(aq)? Zn(NO3)2(aq) Ni(s)

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2. Double Replacement Reactions

• Double Replacement Reactions occur when the
  cations in two compounds switch places.
• compound compound ? compound compound
• AB CD ? AD CB

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Double Replacement Reactions

• KOH H2SO4 ? K2SO4 HOH
• FeS HCl ? FeCl2 H2S
• NaCl H2SO4 ? Na2SO4 HCl
• NH4NO3 NaCl ? NH4Cl NaNO3

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Decomposition Reactions

• Decomposition reactions occur when a compound
  breaks up into two or more substances.
• Some examples of decomposition reactions are
• Potassium chlorate when heated breaks into oxygen
  gas and potassium chloride.
• 2KClO3 ? 2KCl 3O2
• Heating sodium bicarbonate decomposes into sodium
  carbonate and water and carbon dioxide.
• 6NaHCO3 ? 3Na2CO3 3H2O 3CO2

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3. Decomposition Reactions

• The simplest decomposition reactions occur when a
  binary compound breaks up into its elements.
• Compound ? Element Element
• In general AB ? A B
• Example 2 H2O ? 2H2 O2
• Example 2 HgO ? 2Hg O2

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Decomposition Reaction
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This reaction is highly endothermic
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Energy Changes

• Many decomposition reactions involve large
  changes in energy (they are highly endothermic or
  highly exothermic).

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Toluene
A
A
A
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Trinitrotoluene
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Tri-Nitro-Toluene
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Nitroglycerin
Nitroglycerin is a contact explosive (physical
shock can cause it to explode) and it degrades
over time to even more unstable forms. This makes
it extremely dangerous to transport or use.
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Alfred Nobel

• Nobel found that when nitroglycerin was added to
  an absorbent inert substance it became safer.
• He patented this in 1867 as dynamite.

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Alfred Nobel
The Merchant of Death is Dead
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Alfred NobelThe Merchant of Death is Dead

• The erroneous publication in 1888 of a premature
  obituary of Alfred Nobel by a French newspaper,
  condemning him for his invention of dynamite, is
  said to have brought about his decision to leave
  a better legacy after his death.
• The obituary stated "The merchant of death is
  dead" and went on to say, "Dr. Alfred Nobel, who
  became rich by finding ways to kill more people
  faster than ever before, died yesterday.
• In reality the newspaper had instead confused
  Alfred for his brother who had passed away.

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Nobel Prizes

• Nobel signed his last will and testament and set
  aside the bulk of his estate to establish the
  Nobel Prizes.

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Synthesis Reactions

• Synthesis reactions occur when two or more
  substances combine to form a compound.
  (Sometimes these are called combination or
  addition reactions.)
• sulfur trioxide reacts with water to make
  sulfuric acid.
• H2O SO3 ? H2SO4

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4. Synthesis reactions

• The simplest Synthesis reactions occur when two
  elements combine and form a binary compound.
• element element ? compound
• Basically A B ? AB
• Example 2H2 O2 ? 2H2O
• Example Fe Cl2 ? FeCl2

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Synthesis Reaction
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5. Combustion Reactions

• Combustion reactions occur when a hydrocarbon
  reacts with oxygen gas.
• This is also called burning!!!
• The products of combustion are carbon dioxide and
  water.

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Combustion Reactions

• Example
• - CxHy O2 ? CO2 H2O
• Combustion is used to heat homes and run
  automobiles (example octane in gasoline, is
  C8H18).
• Combustion also got you to school today.

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• Cellular Respiration
• C6H12O6 6O2 ?
• 6CO2 6H2O

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Combustion Reactions

• CxHy O2 ? CO2 H2O
• This is an example of complete combustion.
• Products in complete combustion are ALWAYS
  carbon dioxide and water.
• Combustion may also be incomplete in which other
  products will form .

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Complete vs. Incomplete Combustion

• Determined by the amount of oxygen.
• Incomplete combustion occurs when there isn't
  enough oxygen to allow the fuel (usually a
  hydrocarbon) to react completely.

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Incomplete Combustion

• Incomplete Combustion occurs when hydrocarbons
  are burned in limited oxygen
• Either we limit the oxygen available or there is
  simply not enough oxygen think of a car running
  in an enclosed garage.
• we produce carbon monoxide instead of carbon
  dioxide, or in extremely limited oxygen we
  produce pure carbon (soot).
• 2C3H8 7O2 ? 6CO 8H2O (limited oxygen)
• C3H8 2O2 ? 3C 4H2O (extremely limited
  oxygen)

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Complete and Incomplete Combustion

• In most combustion reactions both incomplete and
  complete combustion occur at the same time and so
  we form all the previously mentioned products.
• C9H20 O2 ? CO2 CO C H2O

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Complete and Incomplete Combustion

• We will however consider combustion to be
  complete when predicting the products of
  reactions.
• C9H20 O2 ?
• C9H20 O2 ? CO2 H2O

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Gas Lighting and CO Poisoning

• People who lived in 19th century cities were
  often poisoned by exposure to carbon monoxide
  from illuminating gas, which was a flammable
  mixture of gas suitable for lighting purposes
  that is made from coal and contained extremely
  high levels of CO.  

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• Poe's face has one eye drooping lower than the
  other while his mouth slants the other way. This
  same abnormality can be seen in the faces of
  people poisoned by CO today.  It is caused by the
  effect of repeated CO exposure on facial nerves
  and can be partially if not completely reversed
  with months of daily oxygen therapy.(very high
  levels of CO exposure, in comparison, can cause
  complete paralysis or coma)

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Was Poe suffering from CO poisoning or just a
troubled soul?

• Poe described many symptoms of CO poisoning in
  his letters, poems and tales.
• People poisoned by CO often have the same bizarre
  physical and mental symptoms he describes.

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Homework

• Reaction Type and Balancing Worksheet
• (Due in two days).