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Writing And Balancing Equations

Writing And Balancing Equations. Chemistry Dr. May. The Road To Writing Sentences. Know the alphabet Know vowels and consonants Know how to spell words Know the meaning of words Know sentence structure Know capitalization and punctuation. The Road To Writing Equations.

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Writing And Balancing Equations

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  1. Writing And Balancing Equations Chemistry Dr. May

  2. The Road To Writing Sentences • Know the alphabet • Know vowels and consonants • Know how to spell words • Know the meaning of words • Know sentence structure • Know capitalization and punctuation

  3. The Road To Writing Equations • Know the atomic symbols • Know oxidation numbers of elements • Know the charge on polyatomic ions • Be able to create the correct formulas • Identify the reactants and products • Balance the equation

  4. The Language of Equations Ca(OH)2 + H2SO4  CaSO4 + 2 H2O • The equation above is like a sentence • The compounds Ca(OH)2, H2SO4, CaSO4, and H2O are like correctly spelled and chosen words • The elements Ca, O, H, and S are like the letters of the alphabet

  5. Equations in English Ca(OH)2 + H2SO4  CaSO4 + 2 H2O • One molecule of calcium hydroxide plus one molecule of sulfuric acid yields one molecule of calcium sulfate plus two molecules of water.

  6. Equations Zn + 2 HCl   ZnCl2 + H2 • On the left, Zn and HCl are reactants • On the right, ZnCl2 and H2 are products • The arrow () means “yields” • The up arrow () indicated a gas product • The 2 in front of HCl is a coefficient • The small 2 to the right of H is a subscript

  7. “Skeleton” Equation • Identify the reaction • Zinc reacts with hydrochloric acid to give zinc chloride and hydrogen gas • Determine the correct formulas and write the “skeleton” (unbalanced) equation • Zn + HCl   ZnCl2 + H2 

  8. Coefficients • A coefficient placed before a formula multiplies every atom in that formula by that number 2 H2SO4 • 2 H2SO4means 2 molecules ofsulfuric acid but also • 4 H atoms, 2 S atoms, and 8 O atoms

  9. Conservation Of Mass • A balanced equation contains the same number of each kind of atom on each side of the equation • The balanced equation obeys the Law of Conservation of Mass

  10. Balance The Equation Zn + HCl   ZnCl2 + H2  • Count atoms of each element on each side • Balance each element by placing whole numbers (coefficients) in front of each formula as needed Zn + HCl   ZnCl2 + H2 2

  11. Write Equation • Calcium hydroxide reacts with sulfuric acid to give calcium sulfate and water Calcium = Ca+2 Hydroxide = OH1 Hydrogen = H+1 Sulfate = SO42 Ca(OH)2 + H2SO4  CaSO4 + H2O

  12. Balance Equation Ca(OH)2 + H2SO4  CaSO4 + HOH Count atoms on both sides 1Ca, 2OH, 2H, 1SO4 1Ca, 1OH, 1H, 1SO4 Balance the water Ca(OH)2 + H2SO4  CaSO4 + HOH 2

  13. Write Equation • Aluminum hydroxide plus sulfuric acid gives aluminum sulfate plus water Aluminum = Al+3 Hydroxide = OH1 Hydrogen = H+1 Sulfate = SO42 Al(OH)3 + H2SO4  Al2(SO4)3 + H2O

  14. Balance The Equation Al(OH)3 + H2SO4  Al2(SO4)3 + HOH 1 Al, 3 OH, 2 H, 1 SO4 2 Al, 3 SO4, 1 H, 1 OH 2 Al(OH)3 + H2SO4  Al2(SO4)3 + HOH 2 Al(OH)3 + 3 H2SO4  Al2(SO4)3 + HOH 2 Al(OH)3 + 2 H2SO4  Al2(SO4)3 + 6 HOH

  15. Write The Equation • Propane burns to produce carbon dioxide and water C3H8 + O2 CO2 + H2O The above skeleton equation must be balanced

  16. Balance The Equation C3H8 + O2 CO2 + H2O • First balance the carbons C3H8 + O2 3CO2 + H2O • Next balance the hydrogens C3H8 + O2 3 CO2 + 4H2O • Finally balance the oxygens C3H8 + 5 O2 3 CO2 + 4 H2O 6 + 4 = 10 2 x 5 = 10

  17. Chemical Equations • Chemical equations are the short hand description of a chemical reaction • It tells us: • The reactants and products • The formulas of the reactants and products • The number of molecules of reactants and products • The number of atoms of each element • The number of moles of each substance

  18. The End • This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology • Please send suggestions and comments to rmay@nccvt.k12.de.us

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