rules for balancing equations determine the correct formula for all reactants and products. write...
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Rules for Balancing Equations
• Determine the correct formula for all reactants and products.
• Write the formulas for the reactants on the left side of arrow and the products on the right
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• Count the number of atoms on each side of the reaction. If a polyatomic ion appears unchanged on both sides count it as one unit.
• Balance the elements one at a time using coefficients.
• NEVER CHANGE SUBSCRIPTS TO BALANCE
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Combination reactions
• Two or more substances come together to form a compound
• A + B AB
• Mg + O2 MgO
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CombinationReactions2H2 + O2 =>
2H2O
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Special combination reactions
• A metal oxide and water give a base
• A base is a compound with hydroxide
• K2O + H2O KOH
• CuO + H2O ?
• Right !! Copper(II) hydroxide
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Special combination reactions
• A nonmetal oxide and water give an acid
• An acid is a compound with hydrogen
• SO3 + H2O H2 SO3 and/or H2 SO4
• NO2 + H2O ?
• Right !! Nitric or nitrous acid
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Important fact
•Combination reactions are responsible for acid rain.
•Sulfuric acid, nitric acid and carbonic acid are involved.
•What nonmetal oxides are involved?
•Where do they come from?
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Decomposition reaction• A substance breaks down
forming two or more substances:
• AB A + B
• NI3= N2 + I2
MnO2
• H2O2 H2O + O2
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Single replacement reactions
• A + BC AC + B
• Aluminum + Iron(II) oxide Aluminum oxide + Iron
• 2Al(s) Fe2O3(s) + --> Al2O3(s) + 2Fe(s)
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Single replacement: will it or will it not happen?
•For metals, check the reactivity series
•A more reactive metal will “bump” a less reactive one
Zn + HCl ZnCl2 +
H2
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Single replacement: will it or will it not happen?
• Magnesium is placed in sulfuric acid
• Mg + H2SO4 MgSO4 + H2
• zinc is placed in phosphoric acid
• 3Zn + 2H3PO4 Zn3(PO4)2 + 3H2
• Potassium is placed in contact with aluminum chloride
• 3K+ AlCl33KCl + Al
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Single replacement: will it or will it not happen?• For non metals – look to the
periodic table (as an activity series)
• F is more reactive than Cl
• F2 + HCl HF + Cl2
But –
• Cl2 + HF no reaction
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Write single replacement equations
•Magnesium is added to lead nitrate
• Iron is added to aluminum sulfide
•Sodium is added to calcium carbonate
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Write single replacement equations
•Cl2 + NaI => ?
• I2 + NaCl => ?
•K + NaCl => ? At
I
Br
Cl
F
Group VIIA
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Double Replacement
• Two compounds interact
• The cations trade places
• AB + CD AD +CB
• Na3PO4 + FeCl3 Fe3PO4 + NaCl
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What is the precipitate
•Silver nitrate and sodium hydroxide react:
•AgNO3 + NaOH NaNO3 + AgOH
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Check the solubility tables
AlCl3 + NaOH Al(OH)3 (s) + NaCl (aq)
• How do we know that the aluminum hydroxide is the precipitate? We look at a solubility table
• If the solubility table indicates “I” (insoluble), expect the substance to be a precipitate
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Combustion reactions
• Fuel + oxygen gives carbondioxide, water, and energy
• C3H8 (g) + 5O2 (g) -----> 3CO2 (g) + 4H2O (g)
• Fuels have carbon, hydrogen, and sometimes oxygen
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Organic molecules: The alkanes CnH2n+2
• Methane CH4
• Ethane C2H6
• Propane C3H8
• Butane C4H10
• Pentane (five carbons) C5H12
• Hexane (six carbons) C6H14
• Heptane (seven carbons) C7H16
• Octane (eight carbons) C8H18
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Can you write balanced equations for the combustion of these hydrocarbons?
• Methane (one carbon)
• Ethane (two carbons)
• Propane (three carbons)
• Butane (four carbons)
• Pentane (five carbons)
• Hexane (six carbons)
• Heptane (seven carbons)
• Octane (eight carbons)