Chemical Reactions

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Chemical Reactions

• A basic definition of a chem rxn is
• A Rearrangement of Atoms
• Really - it is substance(s) changing into
  different substances

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Here is an Example

• Notice the motion

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Evidence of Chemical Reactions

• Visual Clues
• A. Color changes
• B. Formation of a solid (precipitate)
• C. Flame occurs
• D. Bubbles are produced (gas)
• Temperature changes
• A. Heat is produced (exothermic)
• B. Heat is absorbed (endothermic)

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An Example

• Eggs, flour, sugar, baking soda, and oil all in
  various amounts
• combine together
• to form Cake!

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A chemical reaction

• The reactants (eggs, flour, etc.) have changed
  and are no longer eggs, flour, etc.
• There is a new substances called a product ?cake
  in this case.

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How do we write these?

• We write these reactions with signs and ?
  signs.
• Eggs Flour Baking Soda Sugar ? Cake

• Be Careful! The Eggs, flour, etc. are not the
  same. They dont exist anymore!!!!

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Another Example

• Hydrogen gas combined with oxygen gas will
  produce dihydrogen monoxide liquid
• H2 O2 ? H2O
• More examples on Help Page

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Why the H2 and O2?!?

• These are called Diatomic Molecules
• Whenever you see hydrogen all by itself, it will
  be paired up!
• There are 7 of them (see Periodic Table)
• There are other examples of this
• Phosphorus all by itself is P4
• Sulfur all by itself is S8

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Phases

• In most cases, phases must also be written. You
  should always include symbols for reactions you
  observe in the laboratory!
• Three common phases
• Solid ex Cu(s)
• Liquid ex H2O(l)
• Gas ex Cl2(g)

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Weird Phases

• Plasma not common
• Aqueous NaCl(aq)
• These are solutions
• Made of water and something dissolved in water
• Mr. Wikrents favorite solution is soda. It has
  many healthy nutrients dissolved in the water of
  each delicious can.
• What is the difference between Cu and Cu2?

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What does a solution look like?

• To the naked eye it looks like a liquid
• Upon closer inspection it is many substances
  mixed together
• See an example
• See another example

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Back to our example

• Hydrogen gas combined with Oxygen gas will
  produce Dihydrogen Monoxide liquid H2
  O2 ? H2O
• Should be
• H2(g) O2(g) ? H2O(l)

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BUT, matter is always conserved, atoms must be
conserved!!!!!!!!
In order to make water, there needs to be 2
hydrogen molecules for every 1 oxygen molecule.
2 H2(g) O2(g) ? 2 H2O(l)
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Lets look back at the Help Pages

• Help Pages

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WE MUST BALANCE!!!

• To correctly write and balance an equation
• 1. Formulas MUST be correct
• 2. There must be the same number of each kind of
  atom on each side of the arrow. This is done by
  using coefficients (numbers in front of a
  formula).
• 3. Do not change formulas to balance atoms!!
• 4. Follow a trial and error process. Balance
  each species one at a time. Be prepared to
  erase!!

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Balancing simple equations

• K Cl2 ? KCl
• Fe O2 ? Fe2O3
• LiCl ? Li Cl2
• NaN3 ? Na N2

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NiO Al ? Al2O3 Ni C4H8 O2 ?
CO2 H2O Ag2O ? Ag O2 B2O3 Mg ?
B MgO KBr Cl2 ? KCl Br2
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Balancing Reactions containing polyatomic atoms

• ExampleLi3PO4 MgCO3 ? Li2CO3 Mg3(PO4)2
• Keep the polyatomic ions together on both sides
• Balance the metal ions first, or if they are
  balanced, the polyatomic ions first, metals last
• If your formulas are correct, the equation
  should balance

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• Balance
• Cu AgNO3 ? Ag Cu(NO3)2
• NaI Pb(NO3)2 ? NaNO3 PbI2
• Ca(CH3COO)2 K2CO3? CaCO3 KCH3COO

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Word equations (writing equations from
observations)

• Water is decomposed by electricity to produce
  hydrogen and oxygen gases through a process
  called electrolysis.
• When copper(II)chloride is dissolved in water and
  reacts with aluminum metal, copper metal and an
  aluminum chloride solution is produced.

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• Lead(II)nitrate solution reacts with sodium
  sulfate solution to produce lead(II)sulfate solid
  and sodium nitrate solution.
• Aluminum iodide solution reacts with lithium
  hydroxide solution to produce aluminum hydroxide
  solid and lithium iodide solution.

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• tetracarbon decahydride (butane) gas reacts with
  oxygen gas to produce carbon dioxide gas and
  water vapor.
• Ammonia gas reacts with oxygen gas to produce
  nitrogen gas and liquid water.

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Remember the following

• Diatomic elements
• hydrogen gas, nitrogen gas, oxygen gas
• AND all halogens in their elemental form
• 2. The formulas and charges of the polyatomic
  ions

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WOW

• The key is that Formulas MUST be correct and
  there must be the same number of each kind of
  atom on each side of the arrow.
• Now go be reactive and produce some good work.
• Assignment is (depending on how well you work)