Transcript STOICHIOMETRY

Proportional Relationships
2 1/4 c. flour
1 tsp. baking soda
1 tsp. salt
1 c. butter
3/4 c. sugar
3/4 c. brown sugar
1 tsp vanilla extract
2 eggs
2 c. chocolate chips
Makes 5 dozen cookies.
I
have 5 eggs. How many cookies
can I make?
Ratio of eggs to cookies
5 eggs 5 doz.
2 eggs
= 12.5 dozen cookies
Mole – Mole Problem
 How
many moles of KClO3 must
decompose in order to produce 9
moles of oxygen gas?
KClO3  KCl + O2
? mol
9 mol O2 2 mol KClO3
3 mol O2
9 mol
= 6 mol
KClO3
Another example
2KClO3  2KCl + 3O2
How many moles of KCl will be
produced if you have 3.1 moles
of O2
QOD #10
You have 0.25 mol of Mg. How
many moles of hydrochloric acid
do you need?
Mg +
HCl
→
MgCl2
+
H2
STOICHIOMETRY
The proportional relationship between two or
more substances (reactants & products) during a
chemical reaction
 Allows you to convert from one unit to another
for different chemicals in a reaction

Mole Ratio:


The coefficients in a balanced chemical reaction
show the # of moles of each substance
Used to convert from moles of one substance to
moles of another
STEPS TO DO STOICHIOMETRY
PROBLEMS
1.
Write the chemical reaction
2.
Balance the chemical reaction (using
coefficients)
3.
Assume the coefficient stands for the # of moles
of each substance
4.
Write out mole-mole ratio in equation
MOLE – MASS PROBLEMS
How many grams of water can be formed from 2.5
moles of ethyne gas (C2H2) reacting with excess
oxygen gas?
C2H2
+
O2
→
H 2O
+
CO2
MASS – MOLE PROBLEM
2 C2H2
+
5 O2
→
2 H 2O
+ 4 CO2
How many moles of O2 must react to produce 12.7g
of CO2 ?
MASS – MASS PROBLEM
If 20.0g of magnesium react with excess
hydrochloric acid, how many grams of
magnesium chloride are produced?
Mg
+
HCl
→
MgCl2
+
H2
QOD #11
A. How many steps would a mol  particle or
mol  volume problem be?
B. How many steps would a mass  particle or
mass  volume problem be?
MASS – PARTICLES PROBLEM
3.47 x 10 26 formula units of potassium sulfate will
make how many grams of mercury (II) sulfate?
K2SO4 +
Hg(NO3)2  KNO3
+
HgSO4
MASS-VOLUME PROBLEM
How many liters of oxygen gas, at STP can be
collected from the complete decomposition of 50.0 g
of potassium chlorate
1. Write
a balanced
equation.
2 KClO
2 KCl(s)
3(s) 
50.0 g
122.55 g/mole
+ 3 O2(g)
? Liters at STP
22.4 L/mole
Writedown
the
“given”
information
from
the
3.2.gWrite
any
information
necessary
1
mole
KClO
50.0
KClO
22.4
L
Oto
3
mole
O
3
3
2
2
=
X to moles. (i.e.
X theunder
X
problem
the
corresponding
change
given measurements
1
KClO3
122.55
g KClO
1 mole O2
3 2 mole
chemical
compound
molar
mass
or
molar
volume
at STP.)
13.71
L go
O2from
gas
6.
“Stoichiometry”
Step.
This
step
allows
you
to
5. Start
Usingthe
the problem
information
under
“given”
and
4.
with
youryour
“given”
over
one.
one compound to another “legally”. Only use the
convert
grams
to moles.
7.coefficients
Convert
moles
unit using
in frontto
ofthe
the appropriate
compounds involved
in the
gathered information, Calculate answer.
problem
MASS TO VOLUME PROBLEM
456L of oxygen gas will react to produce what mass
of water?
___ C6H14 + ___ O2

___ CO2 + ___ H2O
QOD #12
What was the best part of
your weekend???
QOD #13
If 4.78 x 1022 molecules of carbon dioxide is
produced, how many moles of C5H12 must react?
C5H12 +
O2
→
CO2
+
H 2O
VOLUME – VOLUME PROBLEM
If you have 750.0 L of hydrogen gas, how many
liters of nitrogen gas do you need to produce
ammonia?
N2 +
H2
→
NH3
PARTICLE – PARTICLE PROBLEM
Just
like volume – volume can
be made a one step problem, so
can a particle – particle problem.
Mass – Mass is still a 3-step
problem, because the molar
mass of each chemical is always
different!!!
PARTICLE – MOLE PROBLEM
If 4.78 x 1022 molecules of carbon dioxide is
produced, how many moles of C5H12 must react?
C5H12 +
O2
→
CO2
+
H 2O
VOLUME – MOLE PROBLEM
What volume of H2O is produced, if you have 4.2
moles of O2 ?
C5H12 +
O2
→
CO2
+
H 2O
Limiting Reactants
 The
reactant that limits the amount of
products formed in a chemical
reaction
 Also called the limitor
 It will be completely used up in the
reaction
 Other
reactant(s) will have some
amount unchanged or left over
- said to be in excess reactant
 The
quantities of the products formed in a
reaction are always determined by the
quantity of the limiting reactant
 To
1.
2.
3.
determine the limiting reactant:
Write balanced chemical reaction
Calculate the mass of products formed by
each amount of reactant
(do 2 mass ---> mass conversion problems)
The limiting reactant = the reactant that
produces the least amount of product
Ex. Identify the limiting reactant when 1.7g of
sodium reacts with 2.6L of chlorine gas at STP to
produce sodium chloride
___ Na + ___ Cl2 → ___ NaCl

Ex. When 9.00 g of aluminum reacts with excess of
phosphoric acid, 30.0 g of aluminum phosphate is
produced. What is the % yield of this reaction?
2 H3PO4 + 2 Al → 2 AlPO4
+ 3 H2
A reaction is expected to produce 2.6 L of
oxygen gas. In reality, the reaction only
produces 0.9 L of oxygen gas. The
percent yield of the reaction is