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Introduction to:

Introduction to:. Balancing Chemical Equations. Outline. Information in Chemical Equations Why do we have to balance equations?? Human Balancing Act Balancing Chemical Equations - Easy as 1,2,3...4! Practice makes perfect or something along those lines. BIG IDEA of Unit.

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Introduction to:

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  1. Introduction to: • Balancing Chemical Equations

  2. Outline • Information in Chemical Equations • Why do we have to balance equations?? • Human Balancing Act • Balancing Chemical Equations - Easy as 1,2,3...4! • Practice makes perfect or something along those lines...

  3. BIG IDEA of Unit • Chemicals react with each other in predictable ways!

  4. Chocolate Chip Oatmeal Cookies • Turn on oven to 170 degrees C • Place first 5 ingredients in mixing bowl, mixing well after each addition • In cup, dissolve baking soda and hot water, then add in mixing bowl • Add flour, oats, & chocolate chips. Mix well • Drop in spoonfuls onto cookie sheets • Bake in oven until starting to turn golden. • Makes about 50 cookies • Ingredients: • 1 cup butter at room temperature • 1 1/2 cups brown sugar • 1 teaspoon vanilla essence • 1/2 teaspoon baking soda • 1 tablespoon hot water • 1 1/2 cups unbleached flour • 1 1/2 cups rolled oats • 1 1/2 cups chocolate chops

  5. Balanced Chemical Equation • 2 H2(g) + O2(g) → 2H2O (g)

  6. Comparison

  7. Recall (from earlier this class!): • Law of conservation of mass • In a given chemical equation, the mass of the reactants is equal to the mass of the products • Chemical equations obey this law - show all the atoms of the reactants are still present in the products • Coefficients are added before chemical formulas in an equation to ensure that the number of atoms on each side of the arrow are equal (balanced!)

  8. Human Balancing Act 1 • Word equation: sodium + chlorine → sodium chloride • What are the chemical formulas of the reactants and product in this equation?

  9. Human Balancing Act 1 • Na + Cl2 → NaCl • Volunteers needed to balance this equation!

  10. Human Balancing Act 1 • Balanced Equation: 2Na + Cl2 → 2NaCl

  11. Human Balancing Act 2 • A little trickier! • Word equation: zinc + silver nitrate → zinc nitrate + silver • What are the chemical formulas of the reactants and products in this equation??

  12. Human Balancing Act 2 • Zn + AgNO3 → ZnNO3 + Ag • Volunteers to balance equation! • Hint: Because polyatomic ions generally stay intact, you can count them the same way as you count atoms!

  13. Human Balancing Act • Balanced Equation: Zn + 2AgNO3 → Zn(NO3)2 +2Ag

  14. Steps for Balancing Chemical Equations: • EXAMPLE: Write the balanced chemical reaction of magnesium with oxygen. • STEP 1:Write word equation for the reaction • Eg. magnesium + oxygen → magnesium oxide

  15. Steps for Balancing (Continued) • STEP 2: Replace each chemical name with the correct chemical formula. (This is called the skeleton equation) • Eg. Mg + O2 → MgO

  16. Steps for Balancing (Continued) • STEP 3: Count the number of atoms of each type on either side of the arrow. • Eg. Mg + O2 → MgO • 1 Mg atom 1 Mg atom • 2 O atoms 1 O atom

  17. Steps for Balancing (Continued) • STEP 4: Multiply the formulas by an appropriate coefficient until all the atoms are balanced. Keep checking whether the numbers of each type of atom on both sides are balanced. • Eg. MgO (on right) must be multiplied by coefficient 2 to balance oxygen atoms • Mg + O2 →2MgO • Mg (on left) must be multiplied by coefficient 2 so there are two Mg atoms on each side • 2Mg + O2 → 2MgO

  18. Balanced Chemical Equation • The final balanced chemical equation is: • 2Mg + O2 → 2MgO

  19. Something a little more complicated... • Write a balanced chemical equation for the reaction between iron (111) nitrate and sodium hydroxide to produce iron (111) hydroxide and sodium nitrate.

  20. Step-by-Step • STEP 1: iron (111) nitrate + sodium hydroxide → iron (111) hydroxide + sodium nitrate • STEP 2: Fe(NO3)3 + NaOH → Fe(OH)3 + NaNO3 • STEP 3: • Reactants: • 1 Fe atom, 3 NO3 -ions, 1 Na atom, 1 OH - ions • Products: • 1 Fe atom, 1 NO3-ion, 1 Na atom, 3 OH - ions

  21. Ta-da! • STEP 4: Multiply NaOH (reactants) by 3 and NaNO3 (products) by 3 to get final balanced equation • Fe(NO3 ) + 3NaOH → Fe(OH)3 + 3NaOH

  22. Remember... Or at least the key to chemical equations...

  23. Balancing Chemical Equations Summary: • STEP 1: The word equation • STEP 2: The skeleton equation • STEP 3: Count atoms and ions on reactants and products side. Add coefficients! • STEP 4: The balanced equation! • For more assistance, consult pages 233-236 in text!

  24. Time to Practice! • Worksheet on balancing chemical equations!

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