Information given by chemical equations
2 C6H6 (l) + 15 O2 (g)  12 CO2 (g) + 6 H2O (g)
In this equation there are 2 molecules of benzene reacting
with 15 molecules of oxygen to produce 12 molecules of carbon
dioxide and 6 molecules of water.
This equation could also be read as 2 moles of benzene reacts
with 15 moles of oxygen to produce 12 moles of carbon dioxide and
6 moles of water.
Since the relationship between the actual number
of molecules and the number of moles present is
6.02 x 1023, a common factor between all species
involved in the equation, a MOLE RATIO
relationship can be discussed.
Information given by chemical equations
2 C6H6 (l) + 15 O2 (g)  12 CO2 (g) + 6 H2O (g)
The MOLE RATIO for benzene and oxygen is 2 : 15. It can be
written as:
2 moles C6H6
or as
15 moles of O2
15 moles O2
2 moles of C6H6
The MOLE RATIO for oxygen and carbon dioxide is 15 : 12. It can be
written as:
12 moles CO2
or as
15 moles of O2
15 moles O2
12 moles of CO2
NOTE: The MOLE RATIO is used for converting moles of one
substance into moles of another substance. Without the balanced
equation there is no other relationship between two different
compounds.
Using the mole ratio to relate the moles of one compound to the
moles of another compound is the part of chemistry called
STOICHIOMETRY !!!!!
How many moles of oxygen are required to burn 2.40 moles
of ethane, C2H6 (g)
2 C2H6 (g) + 7 O2 (g) → 4CO2 (g) + 6 H2O (l)
2.40 moles C2H6 (g) 7 moles O2
2 mole C2H6 (g)
= 8.40 mole O2 (g)
STOICHIOMETRY !!!!!
2 H2 (g) + O2 (g)  2 H2O (g)
Q. How many mole of hydrogen are
necessary to react with 2 moles of oxygen
in order to produce exactly 4 moles of
water?
A. 2 mol O2 (2 moles H2 / 1 mole O2) = 4 mole H2
STOICHIOMETRY
The Stoichiometry Flow Chart
Use Molar
mass (A)
Mass of A
Use mole
ratio from
equation
mole of A
Use Molar
mass (B)
moles of B
Mass of B
STOICHIOMETRY
2 H2 (g) + O2 (g)  2 H2O (g)
Q1. How many moles of hydrogen are necessary to react with
15.0 g of oxygen?
A. 15.0g O2 (1 mole O2 ) ( 2 mole H2) = 0.938 moles H2
32.0 g
1 mole O
2
Q2. How many grams of hydrogen are necessary to react with
15.0 g of oxygen?
A. 15.0g O2 (1 mole O2 ) ( 2 mole H2) ( 2.016 g H2) = 1.89 g H2
32.0 g
1 mole O
2
1 mole H
2
STOICHIOMETRY
2 H2 (g) + O2 (g)  2 H2O (g)
Q3. How many grams of water are produced from 15.0 g of oxygen?
A. 15.0g O2 (1 mole O2 ) ( 2 mole H2O) ( 18.0 g H2O) =16.9 g H2O
32.0 g
1 mole O
2
1 mole H O
2
Q4. How much hydrogen and oxygen is needed to produce 25.0
grams of water?
A. 25.0g H2O (1 mole H2O ) ( 2 mole H2) ( 2.016 g H2) = 2.80 g H2
18.0 g
2 mole H O
2
1 mole H
2
A. 25.0g H2O (1 mole H2O ) ( 1 mole O2) ( 32.0 g O2) = 22.2 g O2
18.0 g
2 mole H O
2
1 mole O
2
Notice that the Law of Conservation of Mass still applies.
STOICHIOMETRY
Sn (s) + 2Cl2 (g)  SnCl4 (s)
Q1. How many moles of chlorine gas are required to react
with of 1.25 g of metallic tin to produce tin (IV) chloride?
A. 1.25 g Sn (1 mole Sn ) ( 2 mole Cl2) = 0.0210 moles Cl2
119 g Sn
1 mole Sn
Q2. How many grams of tin (IV) chloride are formed from the
reaction of 1.25 g of metallic tin and yellow chlorine gas?
A. 1.25 g Sn (1 mole Sn ) ( 1 mole SnCl4) ( 261 g SnCl4 ) = 2.74 g SnCl4
119 g Sn
1 mole Sn
1 mole SnCl
4
How many grams of solid are formed when 10.0
g of lead reacts with excess phosphoric acid?
1. Write the chemical equation: Pb + H3PO4  ?
You recognize that this is a single displacement (replacement)
reaction. So Pb (a metal) will displace (replace) H (the cation).
Pb + H3PO4  Pb3(PO4)2 + H2
2. Balance the equation: 3 Pb+2 H3PO4  Pb3(PO4)2 + 3 H2
3. Make a list under the appropriate substance
3 Pb+2 H3PO4  Pb3(PO4)2 (s) + 3 H2 (g)
10.0g
m=?
Start with what is given:
10.0gPb (1 mole Pb)( 1 mole Pb3(PO4)2)(811 g Pb3(PO4)2) = 13.1 g Pb3(PO4)2
207 g Pb
3 mole Pb
1 mole Pb (PO )
3
42
PRACTICE PROBLEM # 18
1.
How many grams of gas can be produced from 0.8876 moles of
HgO?
14.20g
2 HgO  2 Hg + O2
2. How many moles of fluorine are required to produce 12.0 grams of
KrF6? Given the equation: Kr + 3 F2  KrF6
0.182 mol
3. How many grams of Na2CO3 will be produced from the thermal
decomposition of 250.0 g of NaHCO3?
157.7 g
4.
How many grams of CO2 can be produced by the reaction of 75.0
grams of C2H2 with excess oxygen?
254 g
5. Cu + 2 AgNO3  Cu(NO3)2 + 2 Ag.
How many grams of silver is produced when 125.0 g of copper is
reacted with excess silver nitrate solution?
424.9 g
GROUP STUDY PROBLEM # 18
______1. How many grams of liquid product can be produced from 3.55
moles of HgO?
2 HgO  2 Hg + O2
______2. How many moles of fluorine are required to produce 3.0 grams
of KrF6? Given the equation: Kr + 3 F2  KrF6
______3. How many grams of Na2CO3 will be produced from the
decomposition of 20.0g of NaHCO3?
______4.
C 2H 4 ?
How many grams of O2 are needed to combust 55.0 grams of
______5. Cu + 2 AgNO3  Cu(NO3)2 + 2 Ag.
How many grams of silver is produced when 50.0 g of copper is reacted
with excess silver nitrate solution?
STOICHIOMETRY
Molar Volume is the volume occupied by one mole of
gas.
Molar volume is different than the molar mass because:
• The molar mass is constant and independent of temperature and
pressure. The molar volume of a gas is variable and is dependent
on the temperature and pressure.
• Each substance has its own unique molar mass. At a given
temperature and pressure, all gases have the same molar volume
• At standard temperature and pressure (STP), the molar volume of
a gas is 22.4 L/mol.
• One mole of any gas at STP occupies 22.4 liters.
Molar Volume Stoichiometry Problems
1. What volume is occupied by 4.21 moles of ammonia gas, NH3
at STP?
4.21 mol
22.4 L = 94.3 L
1 mole
2. What volume of hydrogen, measured at STP, can be released by
42.7 g of zinc as it reacts with hydorchloric acid?
Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 (aq)
42.7 g Zn 1 mol Zn
65.4 g Zn
1 mol H2
1 mol Zn
22.4 L H2 = 14.6 L H2
1 mol H2