Chemistry Learning Targets
Stoichiometry
Chapter 11
Stoichiometry Definition
• The study of the quantitative, or
measurable, relationships that exist in
chemical formulas & chemical
reactions
Student should be able to perform
the following types of stoichiometric
calculations using balanced
chemical equations:
3.18
3.19
3.14
3.15
3.16
mole-mole
mass-mole
mass-mass
mass-volume
volume-volume
Interpreting Balanced Chemical
Equations
• NH4NO3 N2O + 2 H2O
• What do the coefficients represent?
– Moles
1 mole NH4NO3 decomposes to produce
1 mole N2O and 2 moles H2O
– Molecules/Atoms
– Volume if gas at STP
N2(g)
+
H2(g) NH3(g)
• If 4.0 mol of H2 react, how many
moles of NH3(g) will be produced?
(mol to mol)
Na2CO3(s) + HNO3(aq) NaNO3(aq) + CO2(g) + H2O
• How many grams of sodium carbonate are
required to produce 100.0 g of sodium
nitrate? (mass to mass)
1
• How many liters of hydrogen are
formed if 4.00 g of Zn react with
excess hydrochloric acid? (mass-vol)
Zn(s) + HCl(aq) H2(g) + ZnCl2(aq)
Mole – Mole Problems
• NH4NO3 N2O + 2 H2O
• If 3.65 moles of NH4NO3 are decomposed,
how many moles of H2O are produced?
3.65 mol NH4NO3 x 2 mol H2O = 7.30 mol H2O
1 mol NH4NO3
(mole given)
x
(mole ratio) = (moles wanted)
• In the electrolysis of water, 75.0 liters
of oxygen gas are produced. How
many liters of hydrogen are
produced? (vol-vol)
H2O(l)
H2(g) + O2(g)
N2 + H2 →
NH3
• If 4.0 moles of H2 react, how many
moles of NH3 will be produced?
Step 1: Balance the Equation
N2 + 3H2 → 2NH3
Step 2: Determine mole ratio of H2 to NH3
(set up ratio of moles of given on bottom, and moles of what you are
trying to find on top)
Step 3: Set up equation
The HEART of
of all stoichiometry
problems!
How many grams of NH3 are in
2.7 moles?
• Molar mass of NH3
– N = 14 x 1 = 14
–H=1x3 = 3
total = 17 g/mole
2.7 mol NH3 x
17 g NH3
= 45.9 gNH 3
1 mole
4 mole H 2 x
2 mol NH3
= 2.7mol NH3
3 mol H 2
KClO3 → KCl + O2
• What mass of KClO3 do you need to
produce 0.50 mol of O2
Step 1: Balance Equation
Step 2: Determine Mole ratio
Step 3: Set up equation
(always start with what you are given
and set up conversions from that!)
2
Solving Stoichiometric
Problems
•
•
•
•
other types
Mass – mass
Mass – volume
Volume – volume
Mass – Mass problems:
Mass of
x
(g)
given
# mole wanted
1 mole
Moles
Moles of
molar mass
=
x
=
=
of given # moles of given wanted x
molar mass
1 mole
Mole Ratio
From balanced
Chemical Reaction
Mass (g)
of wanted
5. How many grams of sodium carbonate are required to
produce 100.0 g of sodium nitrate?
Na2CO3(s) + HNO3(aq) NaNO3(aq) + CO2(g) +
Mass – Volume problems:
Remember Moles to Liters???
• at STP, 1 mole of a gas = 22.4L
• How many liters are present in 10g of
H2 at STP?
10 g H 2 x
Mass (g)
of given
x
Moles
Moles of
1 mole
# mole wanted
=
x
=
molar mass of given # moles of given wanted
1 mol H 2 22.4 L
x
= 112L
2.0 g H 2 1 mol H 2
Molar mass
of H2
Molar volume
conversion
Volume – Volume Problems
• If a mole of any gas occupies the
same volume as any other gas at
STP (22.4L) then mole ratios are
also volume ratios at STP
N2(g) + 3H2(g) 2NH3(g)
1 liter of Nitrogen gas reacts with 3 liters
of hydrogen gas to produce 2 liters of
ammonia gas.
H 2O
Mole Ratio
From balanced
Chemical Reaction
22.4L
=
1 mole
x
Volume (L)
of wanted
If an airbag contains 125 g sodium azide, NaN3,
what volume of nitrogen gas is produced at
STP? (0oC & 1 atm)
2NaN3 2Na + 3N2
Volume – Volume Problems
Volume of
Given
x
# volume wanted
=
# volume of given
Volume of
Wanted
Volume Ratio
From balanced
Chemical Reaction
What volume of H2 gas reacts with N2 to
form 6.5 L of ammonia?
N2(g) + 3H2(g) 2NH3(g)
3
Summary
Summary
• Stoichiometry is the math of chemical
reactions
• Mole ratios from chemical equations
allow us to convert between amounts
of substances in chemical reactions.
• MUST use balanced chemical
equation in calculations
• Mole ratios are HEART of all
conversion problems and can be used
to:
– Mole to mole
– Mass to mole
– Mass to mass
– Mass to volume
– Volume to volume
4