Transcript An Introduction to Stoichiometry

Stoichiometry
CHEMISTRY 11
MS. MCGRATH
What is Stoichiometry?
The study of the quantities of reactants and products in a
chemical reactions, ie. the amount of reactants that react to
produce a certain amount of products.
The Factor Label Method
Concerting Units
GIVEN unit x WANTED unit = WANTED unit
GIVEN unit
The Factor Label Method - Example
How many seconds are there in 5 minutes?
GIVEN unit x WANTED unit = WANTED unit
GIVEN unit
5 min x 60 sec = 300 sec
1 min
The Factor Label Method - Example
How many centimeters are there in 4.2 kilometers?
The Factor Label Method – Example
How many centimeters are there in 4.2 kilometers?
GIVEN unit x WANTED unit = WANTED unit
GIVEN unit
4.2 km x 10, 000 cm = 420, 000 cm
1 km
The Factor Label Method – You try
1. Convert 42 centimeters to inches. (2.54 centimeters = 1 inch)
2. Convert 50 milliliters to liters. (1000 milliliters = 1 liter)
3. Convert 285 grams to pounds. (454 grams = 1 pound)
4. How many seconds are in 3 days?
5. How many days are in 56, 000 seconds?
6. How many inches are you if you are 2.3 meters tall?
(39.37 inch = 1 meter)
The Factor Label Method - Answers
1. Convert 42 centimeters to inches. 16.53 in
2. Convert 50 milliliters to liters. 0.05 l
3. Convert 285 grams to pounds. 0.63 lb
4. How many seconds are in 3 days? 259, 000 sec
5. How many days are in 56, 000 seconds? 0.65 day
6. How many inches are you if you are 2.3 meters tall? 90.5 in
History of the Mole
• The number 6.022 x 1023 was first proposed by an Italian chemist /
physicist named Amedeo Avogadro
• The mole gets abbreviated as NA and is also known as Avogadro’s
constant
The Mole (mol)
Chemists group large numbers of particles into amounts that are
easily measured. Certain items, because of their size, are often
handled in bulk.
Some common quantities:
Item
gloves
soft drinks
eggs
pens
paper
Quantity
pair
six-pack
dozen
gross (12 dozen)
ream
Amount
2
6
12
144
500
The Mole (mol)
The mol is simply a unit of quantity.
We can have a mol of anything, however it is a convenient way to
group together particles that are too small to count.
The Mole (mol)
• It has been determine that there are 6.02 x 1023 carbon atoms in a
12.00 g sample of carbon-12 (the iostope)
• One mol of sodium chloride contains 6.02 x 1023 formula units of
NaCl (formula units refers to the smallest particle of an ionic
compound)
• One mol of hydrofluoric acid contains 6.02 x 1023 molecules of HF
• A mol of any element contains 6.02 x 1023 atoms of that element
Avogadro`s Constant, NA
• When referring to the mole, it is important to refer to the type of
item (the particle) being identified
• For example, when referring to “a mole of oxygen” it could be
referring to oxygen atoms, oxygen molecules or oxide ions
The Mole and its Conversions
Converting Moles to Number of Particles
The relationship between moles, number of particles and the
Avogadro constant is:
N = n x NA
where:
N = number of particles
n = amount (mol)
NA = Avogadro’s constant (6.02 x 1023)
The Mole and its Conversions
Converting Moles to Number of Particles
Example: Calculate the number of particles (atoms) in 2.0 mol.
N = n x NA
The Mole and its Conversions
Converting Moles to Number of Particles
A sample contains 1.25 mol of nitrogen dioxide, NO2.
a) How many molecules are in the sample?
b) How many atoms are in the sample?
In this case, NA = 6.02 x 1023 molecules / mol
The Mole and its Conversions
Converting Moles to Number of Particles
Try #5, 6 page 51
The Mole and its Conversions
Converting Number of Particles to Moles
Recall the equation we used previously:
N = n x NA
To convert the number of particles to moles we rearrange the
equation.
n=N
NA
Try #12 - 15