Final Information
• Open-ended: 6/11 (review 6/10)
• Last day to ask questions for MC 6/14
• Topics:
– Bonding
– Reactions
• Chemical Equations (balancing, types)
–
–
–
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Percent Composition
Molar Mass, Avogadro’s Number, conversions
Empirical Formula
Stoichiometry
• Limiting reactants
• Mole-mole, grams-grams, particles-particles conversions
Stoichiometry
Atoms or
Molecules
Flowchart
Divide by 6.02 X 1023
Multiply by 6.02 X 1023
Moles
Multiply by
atomic/molar mass
from periodic table
Divide by
atomic/molar mass
from periodic table
Mass
(grams)
Calculations
molar mass
Grams
Avogadro’s number
Moles
particles
Everything must go through
Moles!!!
Chemistry Recipes
Looking at a reaction tells us how much of
something you need to react with
something else to get a product (like the
cookie recipe)
 Be sure you have a balanced reaction
before you start!

2 Na + Cl2  2 NaCl
 This reaction tells us that by mixing 2 moles of
sodium with 1 mole of chlorine we will get 2 moles
of sodium chloride
 What if we wanted 4 moles of NaCl? 10 moles?
50 moles?
 Example:
Example
Questions

Write the balanced reaction for hydrogen gas
reacting with oxygen gas.




2 H2 + O2  2 H2O
How many moles of reactants are needed?
What if we wanted 4 moles of water?
What if we had 3 moles of oxygen, how much hydrogen
would we need to react, and how much water would we
get?
What if we had 50 moles of hydrogen, how much oxygen
would we need, and how much water produced?
Stoichiometry questions (1)
Consider : 4NH3 + 5O2  6H2O + 4NO
• How many moles of H2O are produced if
0.176 mol of O2 are used?
# mol H2O= 0.176 mol O2 x 6 mol H2O = 0.2112
5 mol O2 mol
H2the
O
• How many moles of NO are produced in
reaction if 17 mol of H2O are also produced?
# mol NO= 17 mol H2O x 4 mol NO = 11.33
6 mol H2O mol NO
Notice that a correctly balanced equation is
essential to get the right answer
Stoichiometry questions (2)
Consider : 4NH3 + 5O2  6H2O + 4NO
• How many grams of H2O are produced if 1.9
mol of NH3 are combined with excess oxygen?
# g H2O=
1.9 mol NH3 x 6 mol H2O x18.02 g H2O= 51.4 g
H2O
4 mol NH3 1 mol H2O
• How many grams of O2 are required to
produce 0.3 mol of H2O?
# g O2=
0.3 mol H2O x 5 mol O2 x 32 g O2 = 8 g O2
6 mol H2O
1 mol O2
Mass-Mass Conversions
Most often we are given a starting mass
and want to find out the mass of a product
we will get (called theoretical yield) or how
much of another reactant we need to
completely react with it (no leftover
ingredients!)
 Now we must go from grams to moles,
mole ratio, and back to grams of
compound we are interested in

Mass-Mass Conversion
Ex. Calculate how many grams of
ammonia are produced when you react
2.00g of nitrogen with excess hydrogen.
 N2 + 3 H2  2 NH3

2.00g N2
1 mol N2
2 mol NH3
28.02g N2 1 mol N2
= 2.4 g NH3
17.06g NH3
1 mol NH3
Stoichiometry questions (3)
Consider : 4NH3 + 5O2  6H2O + 4NO
• How many grams of NO is produced if 12 g of
O2 is combined with excess ammonia?
# g NO=
12 g O2 x 1 mol O2 x 4 mol NO x 30.01 g NO
32 g O2
5 mol O2
1 mol NO
= 9.0 g NO
Converting grams to grams
•
Notice that we cannot directly convert from
grams of one compound to grams of another.
Instead we have to go through moles.
• Many stoichiometry problems follow a pattern:
grams(x)  moles(x)  moles(y)  grams(y)
• We can start anywhere along this path
depending on the question we want to answer
Q- for the reaction 2H2 + O2  2H2O what is the
path we would take for the following
• Given 2 moles H2O, calculate grams H2O?
• Moles O2 required for 36 g H2?
• Grams of H2O produced from 6 grams O2?
Moving along the stoichiometry path
•
We always use the same type of information
to make the jumps between steps:
Molar mass of x
Molar mass of y
grams (x)  moles (x)  moles (y)  grams (y)
Mole ratio from
balanced equation
Given: 4NH3 + 5O2  6H2O + 4NO
a) How many moles of H2O can be made using 0.5 mol NH3?
b) what mass of NH3 is needed to make 1.5 mol NO?
c) how many grams of NO can be made from 120 g of NH3?
Answers
4NH3 + 5O2  6H2O + 4NO
a)
# mol H2O= 0.5 mol NH3 x 6 mol H2O = 0.75
mol
4 mol NH3
b)
H
O
2
# g NH3=
1.5 mol NO x 4 mol NH3 x 17.04 g NH3= 25.6 g
NH3
c)
4 mol NO 1 mol NH3
# g NO=
120 g NH3 x 1 mol NH3 x 4 mol NO x 30.01 g NO
17.04g
4 mol NH3 1 mol NO
NH3
=
211 g NO
More Stoichiometry Questions
Follow the rules for significant digits. Show all calculations.
1. 2 C4H10 + 13 O2 -> 8 CO2 + 10 H2O
a) what mass of O2 will react with 400 g C4H10?
b) how many moles of water are formed in a)?
2. 3 HCl + Al(OH)3 -> 3 H2O + AlCl3
How many grams of aluminum hydroxide will
react with 5.3 moles of HCl?
3. Ca(ClO3)2 -> CaCl2 + 3 O2
What mass of O2 results from the decomposition
of 1.00 kg of calcium chlorate?
4. The reaction of Ca with water can be predicted
using the activity series. What mass of water is
needed to completely react with 2.35 g of Ca?
5. Fe2O3 + 3CO -> 2Fe + 3CO2.
a) How many moles of carbon monoxide are
required to react with 163.0 g of iron(III) oxide?
b) How many grams of CO2 are produced from a
reaction that also produces 23.9 grams of Fe?
6.
3Cu + 8HNO3  3Cu(NO3)2 + 4H2O + 2NO
a) how many moles of copper(II) nitrate can be
prepared from 17.0 moles of Cu?
b) how many grams of copper(II) nitrate can be
prepared using 3.8 moles of HNO3?
c) what mass of water results from the reaction of
8.50 kg of copper metal?
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