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•S T U D Y G R O U P S - F I R S T M E E T I N G T H I S W E E K
•E X A M # 1 T H I S W E E K ! F R I D A Y , S E P T E M B E R
1 8 TH
•Addition
to Study Guide:
Given the masses of two reactants and a chemical
equation, be able to determine e which is the limiting
reactant
(Chemical Analysis is not on the exam)
Alum Lab- % Yield Calculation
Limiting Reactants
2H2 + O2  2H2O
 Example: We have 10 mol H2 and 7 mol O2
 What is the number of moles of O2 needed to react
with all of the H2?


1
mol
O
2




mol
O

10
mol
H

5
mol
O
2
2
2


2
mol
H
2


 How much O2 will be left over?
7 mol O2 available- 5 mol O2 needed= 2 mol O2
Limiting Reactants
2H2 + O2  2H2O
 Example: We have 10 mol H2 and 7 mol O2
Limiting Reactants
 If given the amount of starting materials, how do I
determine which is the limiting reactant?
 Two approaches:
Determine the theoretical yield from each
2.
Divide the # moles of each by its stoichiometric #
(In both approaches, the smaller # is the limiting reactant)
1.
Example
 The reaction:
2
SO
(
g
)

O
(
g
)

H
O
(
l
)

2
H
SO
(
a
)
2
2
2
2
4
 We have 5.0 mol SO2, 4.o mol O2, and 10.0 mol H2O.
Which is the limiting reactant?
 What if I started with 5g SO2, 4g O2, and 10g H2O?
Stoichiometry- Limiting Reactants
 100mL 0.1M HCl + coil of Mg in each flask
 Flask 1= 1.2g Mg
 Flask 2= 0.6g Mg
 Flask 3= 2.4g Mg
 The reaction:
Mg

2
HCl

MgC

H
2
2
 Which balloon inflates the most? Least?
 Does half the Mg mean half the H2?
 Does twice the Mg mean twice the H2?