Stoichiometry
ICS III
Week 6
Baking Recipe
• Ingredients
–
–
–
–
–
–
–
–
–
1 cup unsalted butter (B)
1 cup sugar (S)
1 cup brown sugar (Bs)
2 large eggs (E)
1 teaspoon pure vanilla extract (V)
3 cups flour (F)
1 teaspoon salt (Na)
2 cups chocolate chips (Cc)
Bake for 30 minutes @ 375 degrees OF
• Makes up to 50 cookies (Co)
Chemical Reactions
• Chemical reaction
– When bonds are broken and rearranged to
form a new substance
– Reactant(s)
• A substance present at the start of a reaction
• You can have 1 reactant or 1,000 reactants
– Product(s)
• Substance produced in a chemical reaction
• You can have 1 product or 1,000 products
REACTANT 1 + REACTANT 2
Yields
PRODUCT 1 + PRODUCT 2
• Chemical Equation
– A representation of a chemical reaction
• The formulas of the reactants (on the left) are
connected by an arrow with the formulas of the
product (on the right).
Baking Recipe
Reactants
• Ingredients
–
–
–
–
–
–
–
–
–
1 cup unsalted butter (B)
1 cup sugar (S)
Letters are symbols that
indicate a specific
1 cup brown sugar (Bs)
compound. B = butter
2 large eggs (E)
1 teaspoon pure vanilla extract (V)
3 cups flour (F)
1 teaspoon salt (Na)
2 cups chocolate chips (Cc)
Bake for 30 minutes @ 375 degrees OF
• Makes up to 50 cookies (Co)
Product
Chemical Reaction for Baking
Chocolate Chip Cookies
–
–
–
–
–
–
–
–
–
1 cup unsalted butter (B)
1 cup sugar (S)
1 cup brown sugar (Bs)
2 large eggs (E)
1 teaspoon pure vanilla extract (V)
3 cups flour (F)
1 teaspoon salt (Na)
2 cups chocolate chips (Cc)
Bake for 30 minutes @ 375 degrees OF
• Makes up to 50 cookies (Co)
When ever you don’t put a number, it
•Bautomatically
+ S + Bs + Eindicates
+ V + Fonly
+ Na
+ Cc  Co
1 compound
•B + S + Bs + 2E + V + 3F + Na + 2Cc  50Co
• Coefficient
– A number that represents how many compounds are present in a
reaction
Making a Bicycle
+ +
Frame
+
+ 2 wheels + handlebar + 2 pedals
F + 2W + H + 2P --- FW2HP2
Reactants
Product
bicycle
Conservation of Mass
• In a chemical reaction mass and atoms are
conserved in every chemical reaction.
– What ever is on the left must equal what is on the
right.
_?_ g
HCl
Hydrochloric
acid
–
–
40 g
59 g
18 g
+ NaOH  NaCl + H2O
sodium
hydroxide
__ grams + 40 g = 77 g
37 grams
sodium
chloride
water
Stoichiometry
• Stoichiometry
– Calculation of quantities in chemical reactions
– Allows chemists to tally the amounts of
reactants and products using ratios of moles
or representative particles.
• Mole Ratio
– Conversion factor derived from the
coefficients of balanced chemical equations
interpreted in terms of moles
How Stoichiometry Works
• If you react 20 grams of sodium hydroxide
with an excess of hydrochloric acid, how
much water would result?
– You always want to work with moles!
– Go through the steps
• What is given
• What are you looking for?
• How do we get there?
How Stoichiometry Works
• What is given?
– 20 grams NaOH
• What are we looking for?
– Grams water (H2O)
• How do we get there??
– Convert to moles
– Mole ratio
– Convert to grams
Mole Ratio
Moles of wanted compound
Moles of given compound
• The coefficient goes in front
How Stoichiometry Works
What is
given
Convert from
moles to
grams
MOLE
RATIO
Convert from
grams to
moles
What is
wanted
How Stoichiometry Works
•In this reaction, how many grams of Fe2O3 are
required to completely react with 84 grams of CO?
What is
given
Convert from
moles to
grams
MOLE
RATIO
Convert from
grams to
moles
What is
wanted
aG
(given quantity)
bW
(wanted quantity)
aG
(given quantity)
bW
(wanted quantity)
aG
(given quantity)
bW
(wanted quantity)
CH4 + 2O2
CO2 + 2H2O
1. The Equation above shows the reaction of
methane (CH4) burning in the presence of
oxygen. If 32 grams of methane react
completely with oxygen, how many grams of
carbon dioxide (CO2) will be formed?
a)
b)
c)
d)
32 g
44 g
56 g
88g