A Balancing Act

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Chemical Equations

• A Balancing Act
• Physical Science and Chemistry
• High School

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Teacher Page

• Content Chemistry Writing and balancing
  equations
• Grade level High School
• Creator Dorothy Walk
• Curriculum Objectives Writing and balancing
  equations
• MAP Standards SC 1

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Chemical Formulas

• Shorthand way of writing a compound or molecule
• Uses subscripts
• Must be correctly written before balancing
  equations

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Chemical Formulas

• Acetic acid HC2H3O2
• Sodium hydrogen carbonate NaHCO3
• Sodium acetate NaC2H3O2
• Water H20
• Carbon dioxide CO2

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Chemical Equations

• Short hand way of writing a chemical reaction
• Includes products and reactants
• Similar to a recipe
• Must have same elements and number of atoms on
  both sides
• Balance equations using coefficients

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Word Equations

• Using only words to describe a reaction--
• Acetic acid sodium hydrogen carbonate ?
  sodium acetate water carbon dioxide

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Chemical Equation

• Write the correct formulas
• Replace the words with formulas
• HC2H3O2 NaHCO3 ? NaC2H3O2 H20 CO2

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Equation with states

• (s) (l) (g) (aq)
• Solid, liquid, gas, aqueous (water solution)
• HC2H3O2 NaHCO3 ? NaC2H3O2 H20 CO2 becomes
• HC2H3O2(aq) NaHCO3(s) ? NaC2H3O2(aq) H20(l)
  CO2(g)

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Equation with energy

• All reactions involve energy
• Reactants energy gt or lt products energy
• Endothermic and exothermic
• 2H2O(l) energy ? 2H2 (g) O2 (g)
• CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (g) energy

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Balanced Equations?

• H2CO3 (aq) ? H2O (l) CO2 (g)
• NaOH (aq) CO2 (g) ? Na2CO3 (s) H2O (l)

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Why Balance?

• Law of Conservation of Mass Conservation of
  Atoms
• Atoms are not created or destroyed
• Coefficients are used to balance an equation
• 2NaOH (aq) CO2 (g) ? Na2CO3 (s) H2O (l)

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Time to Think and Write

• Why do formulas have to be balanced?
• Why cant subscripts be changed to balance an
  equation?
• Why are some single elements written with the
  subscript 2, such as O2 or N2 or H2?

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Practice writing equations

• Sodium metal chlorine gas yields sodium
  chloride crystals
• Zinc metal hydrochloric acid yields zinc
  chloride solution hydrogen
• Propane gas oxygen yields carbon dioxide
  water vapor energy

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More practice

• 4. Magnesium metal and water combine to form
  solid magnesium hydroxide and hydrogen gas
• 5. When energy is added to solid manganese (II)
  sulfate heptahydrate crystals, they break down to
  form liquid water and solid manganese (II)
  sulfate monohydrate

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Answers

• 2Na (s) Cl2 (g) ? 2NaCl (s)
• Zn(s) 2HCl (aq) ? ZnCl2 (aq) H2 (g)
• C3H8 (g) 5O2 ? 3CO2 (g) 4H2O (g) energy
• Mg(s) 2H2O (l) ?Mg(OH) 2 H2 (g)
• MnSO4.7H2O(s) energy ? 6H2O(l) MnSO4.H2O(s)

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Thinking answers

• 1. Conservation of Matter Law
• 2. Changing formulas change the reaction.
• 3. They are diatomic molecules