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 Chemicals react with each other in predictable ways!

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

Balanced Chemical Equation 2 H 2 (g) + O 2 (g) → 2H 2 O (g)

Comparison Information Communicated RecipeChemical Equation Starting materialsIngredient listReactants Conditions of starting materialsDirections (Ie. butter at room temp)State symbols (g), (s), (l), (aq) Proportions of starting materials Quantities in ingredients list (Ie. 1 cup) Coefficients of reactants (Eg. 2H 2 (g)) Instructions for combining materials Directions (Ie. mixing well after each addition) Plus sign between formulas of reactants, indicating they come into contact Resulting product Title (Ie. Chocolate Chip Oatmeal Cookies) Products Proportions/Quantities of ProductsFinal sentence (Ie. 50 cookies) Coefficients of products (Ie. 2H 2 O (g))

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!)

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

Human Balancing Act 1 Na + Cl 2 → NaCl Volunteers needed to balance this equation!

Human Balancing Act 1 Balanced Equation: 2Na + Cl 2 → 2NaCl

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??

Human Balancing Act 2 Zn + AgNO 3 → ZnNO 3 + Ag Volunteers to balance equation! Hint: Because polyatomic ions generally stay intact, you can count them the same way as you count atoms!

Human Balancing Act Balanced Equation: Zn + 2AgNO 3 → Zn(NO 3 ) 2 + 2Ag

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

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

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

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 + O 2 → 2MgO Mg (on left) must be multiplied by coefficient 2 so there are two Mg atoms on each side 2Mg + O 2 → 2MgO

Balanced Chemical Equation The final balanced chemical equation is: 2Mg + O 2 → 2MgO

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.

Step-by-Step STEP 1: iron (111) nitrate + sodium hydroxide → iron (111) hydroxide + sodium nitrate STEP 2: Fe(NO 3 ) 3 + NaOH → Fe(OH) 3 + NaNO 3 STEP 3: Reactants: 1 Fe atom, 3 NO 3 - ions, 1 Na atom, 1 OH - ions Products: 1 Fe atom, 1 NO 3 - ion, 1 Na atom, 3 OH - ions

Ta-da! STEP 4: Multiply NaOH (reactants) by 3 and NaNO 3 (products) by 3 to get final balanced equation Fe(NO 3 ) + 3NaOH → Fe(OH) 3 + 3NaOH

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

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 in text!

Time to Practice! Worksheet on balancing chemical equations!