introduction to: balancing chemical equations. outline information in chemical equations why do we...
TRANSCRIPT
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...
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
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 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!
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
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!