Stoichiometry: Mathematics of chemical formulas and equations

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!

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 6.02×1023molecules.

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

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?

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