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Writing Chemical Equationsto Symbolize Chemical Reactions

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Solid aluminum metal reacts with oxygen gas to produce solid aluminum oxide.

1. Write the formulas of the reactants and products.

• Al + O2 → Al2O3

2. Add symbols to indicate physical state.

• Al(s) + O2(g) → Al2O3(s)

3. Balance (Law of Conservation of Mass)

• 4Al(s) + 3O2(g) → 2Al2O3(s)

4. Synthesis Reaction

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Electrical current through water.Electrolysis of water into its elements.

1. Write the skeleton equation

• H2O → H2 + O2

2. Put in physical state symbols

• H2O(L) → H2(g) + O2(g)

3. Balance

• 2 H2O(L) → 2 H2(g) + O2(g)

4. Decomposition

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Solid iron rusts. Solid iron reacts with oxygen gas to

produce iron(III) oxide.1. Write the skeleton equation

• Fe + O2 → Fe2O3

2. Put in physical state symbols

• Fe(s) + O2(g) → Fe2O3(s)

3. Balance

• 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)

4. Synthesis (aka combination)

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Ammonium Nitrate dissolves.Since we have defined dissolving as a physical change, this is NOT a chemical reaction, just a physical change.

1. Write the skeleton equation• NH4NO3 → NH4

+ + NO3−

2. Put in physical state symbols• NH4NO3(s) → NH4

+(aq) + NO3

−(aq)

3. Balance• Already balanced.

4. Dissolving

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Aqueous sodium dichromate is reacted with aqueous lead(II) nitrate to produce a solid precipitate of lead(II) dichromate and aqueous sodium nitrate.

1. Write the skeleton equationNa2Cr2O7 + Pb(NO3)2 → PbCr2O7 + NaNO3

2. Put in physical state symbolsNa2Cr2O7(aq) + Pb(NO3)2(aq) → PbCr2O7(ppt) + NaNO3(aq)

3. BalanceNa2Cr2O7(aq) + Pb(NO3)2(aq) → PbCr2O7(ppt) + 2NaNO3(aq)

4. Double Replacement

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Solid potassium metal is reacted with water to produce aqueous potassium hydroxide and hydrogen gas.

1. Write the skeleton equation

• K + H2O → KOH + H2

2. Put in physical state symbols

• K(s) + H2O(L) → KOH(aq) + H2(g)

3. Balance• 2K(s) + 2H2O(L) → 2KOH(aq) + H2(g)

4. Single Replacement

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Solid calcium reacted with liquid water to produce aqueous calcium hydroxide and hydrogen gas.

1. Write the skeleton equation• Ca + H2O → Ca(OH)2 + H2

2. Put in physical state symbols• Ca(s) + H2O(L) → Ca(OH)2(aq) + H2(g)

3. Balance• Ca(s) + 2H2O(L) → Ca(OH)2(aq) + H2(g)

4. Single Replacement

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Solid zinc reacts with aqueous hydrochloric acid to produce aqueous zinc chloride and hydrogen gas.

1. Write the skeleton equation• Zn + HCl → ZnCl2 + H2

2. Put in physical state symbols• Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)

3. Balance• Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

4. Single Replacement

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Burning of methane gas, CH4

1. Write the skeleton equation

• CH4 + O2 → H2O + CO2

2. Put in physical state symbols

• CH4(g) + O2(g) → H2O(g) + CO2(g)

3. Balance

• CH4 (g) + 2O2(g) → 2H2O(g) + CO2(g)

4. This is the gas that comes through our Bunsen burners.

5. Combustion

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Nylon is formed from hexamethylenedamine reacting with sebacoyl chloride to produce the nylon polymer and hydrochloric acid.

1. Nylon is a generic term to represent a particular type of polymer.

• C6H12N2H6 + C6H8Cl2O2 → C12H20O2N2H4 + 2 HCl

2. Balance• C6H12N2H6 + C6H8Cl2O2 → C12H20O2N2H4 + 2 HCl

3. This is a typical polymerization reaction.

• Polymer = many mers (repeating small units)• Polymerization = making polymers from

monomers.

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Polymerization - making large molecules from small units

1. You may remember that many glucose molecules hooked together make the polymer starch or cellulose