Stoichiometry: Mathematics of chemical formulas and equations
MoleMoleMoleMole• A mole is just a number
pair = 2
trio = 3quartet = 4dozen = 12baker’s dozen = 13gross = 144
mole = (mol) 602000000000000000000000
6.02x1023
Avogadro’s Number
9.12 x 1013
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?
• 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 109 years
• If you had a mole of H2O could you swim in it?
NO!Water molecules are so small
that a mole of H2O = 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 1017 molecules
• Each time you take a breath of air, you inhale about 2 x 1022 molecules of nitrogen and 5 x 1021 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!
Gram ATOMic Mass
• mass in grams of 1 mole of atoms of an element
• In other words……
1 mol C atoms = 6.02 x 10 23 C atoms = 12g C
of the
in
Practice
Remember . . .1 mole = 6.02x1023 atoms or
molecules = ______ g from the periodic table
Stoichiometry of Chemical Formulas
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 = 6.02x1023 particles of NaCl
1 mole of H2O = 18g = 6.02x1023 molecules of H20
of the
in
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!
Stoichiometry of Chemical Formulas
• If you have 1 molecule of (NH4)2SO4
– How many atoms of N are there?– How many atoms of H?
SO…..• If you have 1 mole of of (NH4)2SO4
– How many moles of N are there?– How many moles of H?
Practice
Remember . . .1 mole = 6.02x1023 atoms or
molecules = ______ gfm from the pt
Gases ONLY@STP
Molar Volume
• 1 mole of ANY gas
O2 (g)
NH3 (g)
He (g)
contains 6.02 x 1023 molecules andoccupies a volume of 22.4L
•STP
standard temperature & pressure
0oC or 273K
101.3kPa or 1 atm
Remember . . .• Gases also have mass
1 mole of O2(g) = 32g
1 mole of NH3(g) = 17g
we can calculate
Density!
D = m/v
• A sample of oxygen contains 3 moles of particles at STP what is its density?
• 2 steps– Convert moles to mass AND volume– Calculate density
• If mass or volume is given, use it and convert the other……. THEN calculate D!
Remember . . .
1 mole = 6.02x1023 atoms or molecules
= gfm = 22.4L (g)
Stoichiometry 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
6CO2 + 12 H2O + 2804kJ 6O2 + C6H12O6 +6H20
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
Practice
Types of Chemical Reactions
• 2 or more reactants combine to build a single product
General Formula:A + B AB
3H2 + N2 2NH3
SYNTHESIS Reaction
Particle Diagram
DECOMPOSITION reaction
• A compound is broken down into 2 or more simpler substances
General Formula:AB A + B
2H2O 2H2 + O2
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 + CaBr2 Ca + MgBr2
Particle Diagram
DOUBLE REPLACEMENT reaction
• TWO elements switch places during the process of the reaction.
General Formula:AB + CD AD + CB
LiCl + KBr LiBr + KCl
Particle Diagram
Combustion
• Oxygen is always a reactant
• CO2 and H2O are always products
• _______ + O2 CO2 + H2O
Practice
• 2Al + 3CuSO4 Al2(SO4)3 + 3Cu
• 2H2 + O2 2H2O
• C12H22O11 11H2O + 12C
• KCl + AgNO3 KNO3 + AgCl
• CH4 + 2O2 CO2 + 2H2O
The EndThe End