Transcript File

CHEMISTRY
STOICHIOMETRY
PANCAKE
STOICHIOMETRY
CALCULATORS REQUIRED
PERIODIC TABLE REQUIRED
THE KEY TO STOICHIOMETRY –
THE MOLE RATIO
• 2Al2O3(l)  4Al(s) + 3O2(g)
• Mole ratios allow us to “convert” between
different reactants and products.
• What is the mole ratio between Al2O3 and Al?
• 2 mol Al2O3 : 4 mol Al
• We can write this as a conversion factor:
 2m olAl2O3 


 4m olAl 
• We can now “convert” between amounts of
different compounds.
ONE CONVERSION: MOL  MOL
• CO2(g) + 2LiOH(s)  Li2CO3(s) + H2O(l)
• How many moles of lithium hydroxide are
required to react with 20 mol CO2?
• Molar ratio between CO2 and LiOH?
• 1:2
YOU TRY: MOL  MOL
• How many moles of chlorine gas (Cl2)
would react with 5 moles of sodium (Na)
according to the following chemical
equation?
• 2 Na + Cl2  2 NaCl
MASS-MASS STOICHIOMETRY
• We just converted between moles of
one substance into moles of another
substance using a chemical reaction.
• In practice, it is more common to
convert from grams of one substance
to grams of another.
• We have to use the mole as a bridge.
• How do we convert between grams
and moles?
STOICHIOMETRIC SETUP
•A  2B
• In order to convert between grams of A and
grams of B, you have to use molar masses
and the molar ratio as conversion factors.
• If you are not given a reaction, you must
generate it yourself!
• grams A  moles A  moles B  grams B
(molar mass A)
(molar ratio)
(molar mass B)
• It is very important to analyze the
problem to figure out how many steps to
use!
• You can start and end at any point on this
bridge!!
SAMPLE PROBLEM 2
• What number of moles of O2 are needed to
produce 14.2 grams of P4O10 from P? (molar
mass of P4O10 = 284 g/mol)
P + O2  P4O10 (unbalanced)
SAMPLE PROBLEM 3
• 2NaCl  2Na + Cl2
• How many grams of chlorine gas are
produced if 60 grams of sodium chloride
are exposed to an electric current?