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Introduction Introduction to:to:

Balancing Chemical Equations

Outline 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 UnitBIG IDEA of UnitChemicals react with each other in predictable ways!

Chocolate Chip Chocolate Chip Oatmeal Cookies 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 Balanced Chemical EquationEquation

2 H2 (g) + O2

(g) → 2H2O (g)

ComparisonComparisonInformation

CommunicatedRecipe Chemical Equation

Starting materials Ingredient list Reactants

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. 2H2(g))

Instructions for combining materials

Directions (Ie. mixing well after each addition)

Plus sign between formulas of reactants, indicating they come

into contact

Resulting productTitle (Ie. Chocolate Chip

Oatmeal Cookies)Products

Proportions/Quantities of Products

Final sentence (Ie. 50 cookies)Coefficients of products (Ie.

2H2O (g))

Recall Recall (from earlier this class!)(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 Human Balancing Act 11

Word equation: sodium + chlorine → sodium chloride

What are the chemical formulas of the reactants and product in this equation?

Human Balancing Act Human Balancing Act 11

Na + Cl2 → NaCl

Volunteers needed to balance this equation!

Human Balancing Act Human Balancing Act 11

Balanced Equation: 2Na + Cl2 → 2NaCl

Human Balancing Act Human Balancing Act 22

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 Human Balancing Act 2 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!

Human Balancing ActHuman Balancing Act

Balanced Equation: Zn + 2AgNO3 → Zn(NO3)2

+ 2Ag

Steps for Balancing Steps for Balancing Chemical Equations: 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 Steps for Balancing (Continued)(Continued)

STEP 2: Replace each chemical name with the correct chemical formula. (This is called the skeleton equation)

Eg. Mg + O2 → MgO

Steps for Balancing Steps for Balancing (Continued)(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

Steps for Balancing Steps for Balancing (Continued)(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

Balanced Chemical Balanced Chemical EquationEquation

The final balanced chemical equation is:

2Mg + O2 → 2MgO

Something a little Something a little more complicated... 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-StepStep-by-StepSTEP 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

Ta-da! 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

Remember... Remember...

Or at least the key to chemical equations...

Balancing Chemical Balancing Chemical Equations Summary: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!

Time to Practice! Time to Practice!

Worksheet on balancing chemical equations!