Stoichiometry: Chemical Reactions are like Recipes How much reactant is needed to make a certain amount of product?
Jan 11, 2016
Stoichiometry: Chemical Reactions are like Recip
es
How much reactant is needed to make a certain amount of
product?
Dozen = 12
Case = 24
Ream = 500
Units A dozen eggs = 12 eggs A case of coke = 24 cans A ream of paper = 500 sheets A century = 100 years
In Chemistry, we use…Mole: It is a unit equal to 6.022 x 1023 ato
ms or molecules
This number is called Avogadro’s Number, in honor of Amadeo Avogadro.
How Big is a Mole?
-One mole of marbles would cover the entire Earth (oceans included) for a depth of three miles.-One mole of $100 bills stacked one on top of another would reach from the Sun to Pluto and back 7.5 milliontimes.
Molar Mass Molar Mass: The mass of 1
mole of substance. 1 mole of carbon contains
6.022 x 1023 atoms and has a mass of 12.0107 grams. Unit: g/mol Carbon’s molar mass is 12.01
g/mol
Molar Mass
ZnCl2:
1 Zn: 1 x 65.39 g/mol = 65.39 g/mol
2 Cl: 2 x 35.45 g/mol = 70.90 g/mol
Molar Mass: 136.29 g/mol
Molar Mass
ZnSO4:
1 Zn: 1 x 65.39 g/mol = 65.39 g/mol
1 S: 1 x 32.07 g/mol = 32.07 g/mol
4 O: 4 x 16.00 g/mol = 64.00 g/mol
Molar Mass = 161.46 g/mol
General Plan for Converting Mass, Amount, and Number of Particles
Mass of
substance
(grams)
Amount of
Substance in
Moles
Number of Atoms
or molecule
s
Use the molar mass
Use Avogadro
’s Number
Sample Problem 1.
A chemist has a jar containing 388.2 g of iron. How many moles of iron does the jar contain?
Sample Problem 2.
A student needs 0.366 mol of zinc for a reaction. What mass of zinc in grams should the student use?
Sample Problem 3.
How many moles of lithium are there in 1.204 x 1024 lithium atoms?
Chemical Equations are like
Cooking Recipes
Recipe makes 5 dozen cookies.
Velasquez has 5 eggs. How many dozens of cookies can she make?
3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chips
2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar
5 eggs 5 doz.
2 eggs= 12.5 dozen cookies
“Mole Ratio” of eggs to cookies
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Recipe makes 5 dozen cookies.
Henkels has 9 cups of chocolate chips. How many dozens of cookies can he make?
3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chips
2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar
5 eggs 5 doz.
2 eggs= 12.5 dozen cookies
“Mole Ratio” of eggs to cookies
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Proportional Relationships: S’more Activity2 Gc + 1 M + 4 Cp 1 Sm
If each student is to make one S’more, and I have 30 students, how many graham crackers & chocolate pieces will I need?
Given: 30 S’moresUnknown: ? Gc, ? Cp
30 S’mores 2 Gc
1 S’more
= ?
“Mole Ratio”
30 S’mores 4 Cp
1 S’more
= ?
“Mole Ratio”
Stoichiometry Diagram
Mass
Particles
VolumeMole
Mole
Mass
Volume
Particles
Given Unknown Substance A Substance B
Use periodic table
1 mole = m
olar mass (g)
Mole RatioUse coefficientsfrom balanced
chemical equation
1 mole = 22.4 LSTP
1 mol
e =
6.0
22 x 1
023 p
artic
les
(ato
ms or
mol
ecule
s)
1 mole = 22.4 L STP1 m
ole = 6.022 x 10 23
particles
(atoms or m
olecules)
Use p
erio
dic ta
ble
1 mol
e =
mol
ar
mas
s (g)
(gases) (gases)
Mole Ratio2Al2O3(l) 4Al(s) + 3O2(g)
2 molecules 4 atoms 3 molecules2 dozen 4 dozen 3 dozen2 moles 4 moles 3
moles-The coefficients of this equation tells us that for every
2 moles of aluminum oxide, it produces 4 moles of solid aluminum and 3 moles of oxygen molecules.
-The mole ratio, a conversion factor between two amounts in a chemical reaction. It is indicated by the coefficients of the chemical equation.
Mole Ratios:2 mol Al2O3 4 mol Al4 mol Al 2 mol Al2O3
2 mol Al2O3 3 mol O2
3 mol O2 2 mol Al2O3