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Class Notes on Stoichiometry
Name _______
CHAPTER 9 – STOICHIOMETERY
STOICHIOMETERY-
The study of the amount of a substances consumed and produced in chemical
reactions.
The science of reactions is basically like cooking. You must
mix the right proportion of each ingredient (reactant) to obtain the best
results (products).
The “recipe” for a chemical reaction is the balanced
equation.
For Example: 2 H2 + O2
→
2H2O
This
can be read as 2 hydrogen molecules mix with one oxygen molecule
to produce 2 water molecules.
or
2 moles of H2 mix with
1 mole of O2 to make 2 moles of H2O
Example:
___KClO3 → ____KCl
+ ____O2
mole ratio step
____moles of KClO3 yields ____ moles of KCl and ____ moles of O2.
You will use these coefficients (mole ratios) to determine how much you will need to mix together or
how much you can produce.
Example of Mole/Mole problems:
1)
How many moles of O2 will 9.5 moles of KClO3
produce?
To solve this problem, we will use
the T-bar and add a mole ratio
step. The mole ratio allows you to convert from one substance to another.
They are the whole number coefficients that you use to balance the equations.
given mole ratio
9.5 moles
KClO3 3 moles of O2____ = 14.25 moles O2
2 moles of
KClO3
Try these two on your own:
1) If
you want to produce 15.0 moles of O2, how many moles of KClO3
should you start with?
2). If 18.2 moles of O2 are produced,
how many moles of KCl are produced with it?
The real key to stoichiometry is
to obtain numbers we can use in the lab. So, instead of moles, we will want our
answers in grams. This requires a conversion from moles to grams using the gfm.
( remember: 1 mole = gfm (gram formula mass )
There are four basic
stoichiometry reactions. Let’s name them
and write the formulas:
1) mole
to mole
2) mole
to mass
3) mass
to moles
4) mass to mass
Now that we have to four basic
types of stoichiometery formulas, lets practice.
CaC2
+ 2 H2O →
C2H2 + Ca(OH)2
Moles-mass problems:
1) How
many grams of water are required to produce 1.55 moles of C2H2?
2) How
many grams of C2H2 are produced when 5.0 moles of CaC2
reacts completely?
Mass-moles problems:
1) How
many moles of water are needed to react with 20.5 g of CaC2?
2) How
many moles of Ca(OH)2 are produced with 29.0 g of C2H2?
3) How
many moles of CaC2 will produce 15.0 g of Ca(OH)2?
The final step in stoichiometry is to start with grams and to end with grams. This way
you know what you are going to produce in lab, or how much of each reactant you
need to mix.
4
Na + O2 → 2 Na2O
1). How many grams of
O2 are required to react completely with 14.6 g of Na to form Na2O?
2). How many grams of
Na2O are produced when 20.0 g Na reacts completely?
3). How many grams of
Na are needed to produce 200.0 g of Na2O?
Mole – mole
conversions
____CaC2 + ____ H2O →
____C2H2
+ ____ Ca(OH)2
1)
How many moles of water are needed to react with 2.5
moles of CaC2?
2)
How many moles of C2H2 are produced when 9.5 moles of
CaC2 are mixed with excess water?
___________________________________________________________________________
____Na + ____ O2 →
____Na2O
3)
How many moles of Na are needed to produce 0.25 moles
of Na2O?
4)
How many moles of O2 will react with 9.4
moles of Na to produce Na2O?
5)
Calculate the number of moles of Na2O that will be
produced when 5.0 moles of Na completely react with oxygen gas?
___C2H6
+ ____O2 →
____ CO2 + ____H2O
6)
How many moles of carbon dioxide are produced when 5.8
moles of C2H6 react completely with oxygen?
7)
How many moles of O2 are needed to react
completely with 18.0 moles of CO2?
8)
How many moles of C2H6 are needed
to produce 14.0 moles CO2?
9)
If 9.8 moles of CO2 are produced, how many
moles of water are also produced?
Gram-mole, Mole –gram conversions
____C2H6
+ ____O2 →
____CO2 + ____H2O
1)
How many grams of CO2 are produced when you
use 8.0 moles of C2H6?
2)
If 8.0 moles of CO2 are produced in this
reaction, how many grams of O2 have been used?
3)
45.0 grams of C2H6 will react
with oxygen to produce ______ moles of water?
____Cu + ____AgNO3 →
____Cu(NO3)2
+ ____Ag
4)
How many moles of AgNO3 are needed to react
with 170.0 g of Cu?
5)
In a reaction, 8.5 moles Ag are produced. How many
grams of Cu were used up in the reaction?
_________________________________________________________________________________
____NH3 + ____NO
→ ____N2 + ____H2O
6)
If 4.5 moles of water are produced, how many grams of
NH3 must you start with?
7)
How many moles of NO are needed to react with 48.0 g NH3?
8)
If 9.8 g of N2 are produced, how many moles
of water are also produced?
9)
How many moles are NH3 will produce 15.0 g of N2?
Gram-Gram conversions
___Li3N + ____H2O →
____NH3 + ____LiOH
1)
What mass of water is needed to react with 98.7 g of
lithium nitride?
2)
How many grams of ammonia will be formed if 36.0 g Li3N reacts completely with
water?
____SiO2 +
____C → ____SiC
+ ____CO
3)
How many grams of SiO2 are needed to react
with 45.0 g of C?
4)
If 19.0 of C are used, how many grams of SiC can be produced?
____NH4NO3
→ ____N2 +
_____O2 + ____H2O
5)
How many grams of water are produced when 45.6 g of
ammonium nitrate decomposes?
6)
If 15.5 grams of O2 are formed, how many grams of NH4NO3
must have decomposed?
7) If 87.5 g of N2 are produced, how
many grams of water are also produced?
