Chapter 12
Stoichiometry
part 1
Stoichiometry
The study of quantitative
relationships between amounts of
reactants used and products formed
by a chemical reaction
Stoichiometry
•
•
Calculations of quantities in
chemical reactions
This means using balanced
equations to calculate quantities
of chemicals used in a chemical
reaction
Law of Conservation of Mass
•
Matter is neither created nor destroyed in
a chemical reaction
• Chemical bonds in reactants break and
new chemical bonds form to produce
products
• Mass of reactants equals the mass of the
products
A chemical equation is like a
recipe; it shows you how much
of each “ingredient” is used and
how much product you will have
in the end.
The heart of stoichiometry is
using a balanced chemical
equation as a conversion
factor for dimensional
analysis.
N2 + 3H2  2NH3
• How many molecules of N2 are there?
• How many molecules of H2 are there?
• How many molecules of NH3 are there?
So one molecule of N2 will react with 3
molecules of H2 to form 2 molecules of
NH3.
You could also say that one mole of N2 will
react with 3 moles of H2 to form 2 moles of
NH3.
• This equation tells the proportions of N2,
H2, and ammonia
• The coefficients are in a 1:3:2 ratio
• The ratio could mean molecules or moles of
each
Review
6.02 x 1023 particles
1 mole
molar mass
1N2(g)
1 mole
28.00g
+
3H2(g)
2NH3(g)
3 moles
3(2.02)=6.06g
2 moles
2(14.00+3.03)=34.06g
Steps to solve every problem:
1) Write a balanced equation.
2) Put what you have over 1.
3) Convert into moles.
4) Compare using the equation.
5) Convert into the unit the
question asks for.
Mole to Mole conversions:
Conversion factor (as with any conversion factor, units
must cancel)
Moles of known x moles of unknown = moles unknown
Moles of known
Mole to Mass conversion:
The mole ratios of the balanced equation is known,
and you’re given a quantity in moles, now find the
mass of another product or reactant.
Burning of propane gas:
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
How much oxygen is needed to
produce 18 mol of CO2?
Zn + HCl  ZnCl2 + H2
• For the above reaction, how many moles
of zinc chloride can be produced with 0.27
moles of zinc?
• For the above reaction, how many moles
of zinc will react with 1.39 moles of
hydrochloric acid?
Fe + O2  Fe2O3
• How many grams of iron (III) oxide can be
produced with 17.2g Fe?
• How many molecules of O2 are needed to
produce 3.92g Fe2O3?
Mass to Mass conversion:
Again, the mole ratios of the balanced
equation is known and you’re given a
quantity in grams, now find the mass of
another product or reactant.
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
67.02g propane would produce ? grams of
water vapor?