Stoichiometry with a Twist
• Given the density of oxygen is 1.439 grams
per liter, how many liters of oxygen gas can
be produced if 15.0g of mercury (II) oxide
are heated to produce mercury and oxygen
gas?
2HgO  2Hg +O2
? L O2 = 15.0g HgO
1 mol HgO
1 mol O2
32g O2
1 L O2
217g HgO
2 mol HgO 1 mol O2 1.439g O2
= 0.770 L O2
Episode 803
Stoichiometry Problem Guidelines
1. Balance the equation
2. Convert to moles of given substance
3. MAKE THE SWITCH USING THE
MOLE RATIO FROM THE BALANCED
EQUATION
4. Convert to desired unit
Problem Set 1
C5H12 + 8 O2  5 CO2 + 6 H2O
• Given that the density of carbon dioxide is
approximately 1.99 g/L, what volume, in liters, of
carbon dioxide will be produced if 85.0g of pentane
are burned?
? L CO2 = 85.0g C5H12 1 molC5H12 5 molCO2 44gCO2
1 L CO2
72gC5H12 1 molC5H12 1 molCO2 1.99gCO2
= 131 L CO2
• How many molecules of water will be produced if
26.3g of pentane are burned?
? molc H2O = 26.3g C5H12 1 molC5H12 6 molH2O 6.02 x 1023 molc H2O
72gC5H12 1 molC5H12 1 molH2O
= 1.32 x 1024 molecules H2O
• Limiting Reactant
– Reactant used up first in a chemical
reaction
– Produces the smallest amount of product
• Excess Reactant
– Reactant that is not used up in a chemical
reaction
– Leftover when the reaction is complete
• When FeCl3 reacts with O2, Fe2O3 and Cl2 are
produced. If 4.0 moles of FeCl3 and 4.0 moles
of O2 are mixed, how many grams of Fe2O3
will be produced?
4FeCl3 + 3O2  2Fe2O3 + 6Cl2
(Hint: Work two separate problems, using one reactant at a time.)
? g Fe2O3 = 4.0mol FeCl3 2mol Fe2O3 160g Fe2O3 = 320g Fe O
2 3
4.0mol FeCl3 1mol Fe2O3
? g Fe2O3 = 4.0mol O2 2mol Fe2O3 160g Fe2O3
3mol O2
1mol Fe2O3
= 430g Fe2O3
(Hint: Answer will be the SMALLER amount of product.)
What is the limiting reactant?
What is the excess reactant?
FeCl3
O2
• Iron(III) oxide reacts with carbon monoxide to
form molten iron and carbon dioxide. If 0.18g of
iron(III) oxide and 0.11g of carbon monoxide, how
many grams of iron are produced?
Fe2O3 + 3CO  2Fe + 3CO2
(Hint: Work two separate problems, using one reactant at a time.)
(Hint: Answer will be the SMALLER amount of product.)
? g Fe = 0.18g Fe2O3 1mol Fe2O3 2mol Fe
56g Fe
= 0.13g Fe
160g Fe2O3 1mol Fe2O3 1mol Fe
? g Fe = 0.11g CO 1mol CO 2mol Fe 56g Fe
28g CO 3mol CO 1mol Fe
What is the limiting reactant?
What is the excess reactant?
= 0.15g Fe
Fe2O3
CO