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