Stoichiometry:
Mathematics of chemical formulas and equations

mole = (mol) 602000000000000000000000
Mole
• A mole is just a number pair = 2 trio = 3 quartet = 4 dozen = 12 baker’s dozen = 13 gross = 144

Avogadro’s Number
6.02x10
23

How BIG is a mole?
There are ~ 6.6 billion people on Earth
How many Earths would it take to equal the population of 1 mole?
9.12 x 10 13

• If you had a mole of cats . . .
They would create a sphere larger than Earth!

• If you had a mole of $$$$$ and you spent
$800 billion dollars a day how many years would it take to spend a MOLEion dollars?
2.06 x 10 9 years

• If you had a mole of H
2 it?
O could you swim in
NO!
Water molecules are so small that a mole of H
2
O = 18ml

How small are atoms?
• There are more atoms in one gram of salt than grains of sand on all the beaches of all the oceans in all the world.

• Just one granule of sugar contains 1 x 10 17 molecules
• Each time you take a breath of air, you inhale about 2 x 10 22 molecules of nitrogen and 5 x 10 21 molecules of oxygen.

• In chemistry we don’t work with individual atoms or molecules because they are too small to be weighed or measured
• We have to work with
LOTS of atoms in order to measure them
THAT’s WHERE THE
MOLE
COMES IN!

The number of grams in a mole is different from substance to substance.
If you're like most students, it's this that's confusing you. Picture it this way: a dozen elephants have a different weight than a dozen rabbits- but in each case, you have a dozen animals.
Similarly, a mole of oxygen gas has a different weight than a mole of water- but in each case, you have 6.02
× 10 23 molecules.

Why use moles?
You often want to know how many molecules you have in a sample of a substance. Counting the molecules individually would be completely impractical.
Even if you had a way to see the individual molecules, there are just too many, even in a tiny sample.
Moles were defined to solve the problem of counting large numbers of molecules. With moles, you count the number of molecules in the sample by weighing it.

Gram ATOMic Mass
• mass in grams is equal to 1 mole of atoms of an element
• In other words……
1 mol C atoms = 6.02 x 10 23 C atoms = 12g C

Practice
Remember . . .
1 mole = 6.02x10
23 atoms or molecules
= ______ g from the periodic table

iometry

Gram Formula Mass
Gram Molecular Mass
Molar Mass
• mass in grams of 1 mole of a substance
• In other words . . . Add it all up!
1 mole of NaCl = 58g = 6.02
x
10 23 particles of NaCl
1 mole of H
2
O = 18g = 6.02x10
23 molecules of H
2
0

Now…..
• Use the gram formula mass and the gram atomic mass to determine
– how many moles or atoms of an element are found in some mass of a substance
– how much mass that element contributes to the mass of the entire substance
Use factor label & follow the units!

Stoich iometry of Chemical Formulas
• If you have 1 molecule of (NH
4
)
2
SO
4
– How many atoms of N are there?
– How many atoms of H?
• If you have 1 mole of of (NH
4
)
2
SO
4
– How many moles of N are there?
– How many moles of H?

Stoich iometry of Chemical
Equations
• The study of quantitative relationships that can be derived from chemical equations.
“it’s a simple matter of weight ratios . . .”

Stoichiometry cookies
• If you look at chemical equations as recipes it may be easier to understand that
– changing the amount of a reactant will change the amount of the product IN THE
SAME RATIO !

Examining Molar Relationships in
Balanced Equations
6CO
2
+ 12 H
2
O + 2804kJ  6O
2
+ C
6
H
12
O
6
+6H
2
0
Balanced equations
– Law of conservation of mass / matter
• ATOMS are not created or destroyed during a chemical reaction, they are only rearranged to form new substances.
• # atoms on reactant side = # atoms on product side
– Law of conservation of E
• E on the reactant side = E on the product side

Mole - Mole Relationships

SYNTHESIS Reaction
• 2 or more reactants combine to build a single product
General Formula:
A + B  AB
3H
2
+ N
2
 2NH
3

Particle Diagram


DECOMPOSITION reaction
• A compound is broken down into 2 or more simpler substances
General Formula:
AB  A + B
2H
2
O  2H
2
+ O
2

Particle Diagram


SINGLE REPLACEMENT reaction
• One of the reactants is a single element. It becomes part of a compound as a product.
General Formula:
A + BX  B + AX
Mg + CaBr
2
 Ca + MgBr
2

Particle Diagram


DOUBLE REPLACEMENT reaction
• TWO elements switch places during the process of the reaction.
General Formula:
A B + CD  A D + C B
Li Cl + KBr  Li Br + K Cl

Particle Diagram


Combustion
• Oxygen is always a reactant
• CO
2 and H
2
O are always products
• _______ + O
2
 CO
2
+ H
2
O

Practice
• 2Al + 3CuSO
4
 Al
2
(SO
4
)
3
+ 3Cu
• 2H
2
+ O
2
 2H
2
O
• C
12
H
22
O
11
 11H
2
O + 12C
• KCl + AgNO
3
 KNO
3
+ AgCl
• CH
4
+ 2O
2
 CO
2
+ 2H
2
O