Thursday
February 7, 2013
(Discussion and WS
– Limiting Reactant)
Bell Ringer
Thursday, 2-7-13
A baker has a recipe for a cake that calls for the following ingredients:
•4 cups of flour
•2 cups of sugar
•1 tsp of baking soda
•1 tsp of baking powder
•1 cup of milk
The baker finds she has the following supplies in her store room:
•17 cups of flour
•9 cups of sugar
•6 tsp of baking soda
•5 tsp of baking powder
•3 cups of milk
3
Without going to the grocery store, how many cakes can she make?
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Summative
or
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Date
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Final Day
QUIZ 16
S1
1/18
1/18
1/24
TODAY
WS – Mole to Mass
Stoichiometry
F11
1/30
2/1
TOMORROW
WS – Mass to Mole
Stoichiometry
F12
1/31
2/5
TOMORROW
QUIZ 17
S2
2/1
2/1
WS – Mass to Mass
Stoichiometry
F13
2/4
2/8
TOMORROW
Activity - Using
Stoichiometry to
Prove the Law of
Conservation of
Mass
F14
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2/5
TOMORROW
2/1
2/15
Limiting Reactant
•In the laboratory, a reaction is rarely
carried out with exactly the required
amounts of each of the reactants.
•In most cases, one or more reactants is
present in excess; that is, there is more
than the exact amount required to
react.
•Once one of the reactants is used up,
no more product can be formed.
Limiting Reactant
• The substance that is completely used up
first in a reaction is called the limiting
reactant.
• The limiting reactant is the reactant that
limits the amounts of the other reactants
that can combine and the amount of
product that can form in a chemical
reaction.
• The substance that is not used up
completely in a reaction is sometimes called
the excess reactant.
Limiting Reactant
• Consider the reaction between carbon
and oxygen to form carbon dioxide.
C + O2 → CO2
• According to the equation, one mole of
carbon reacts with one mole of oxygen to
form one mole of carbon dioxide.
• Suppose you could mix 5 mol of C with
10 mol of O2 and allow the reaction to
take place.
Limiting Reactant
•
•
•
The figure below shows that there is more oxygen
than is needed to react with the carbon.
Carbon is the limiting reactant in this situation, and
limits the amount of CO2 that is formed.
Oxygen is the excess reactant, and 5 mol of O 2 will be
left over at the end of the reaction.
Limiting Reactant
Sample Problem
Silicon dioxide (quartz) is usually quite unreactive, but reacts
readily with hydrogen fluoride according to the following
equation:
SiO2 + 4HF → SiF4 + 2H2O
If 2.0 mol of HF are exposed to 4.5 mol of SiO 2,
which is the limiting reactant?
Answer - The given amount of either reactant is used to calculate
the required amount of the other reactant. The calculated
amount is then compared with the amount actually available, and
the limiting reactant can be identified. We will choose to calculate
the moles of SiO2 required by the given amount of HF.
Limiting Reactant
Sample Problem
SiO2 + 4HF → SiF4 + 2H2O
Under ideal conditions, the 2.0 mol of HF will require
0.50 mol of SiO2 for complete reaction. Because the
amount of SiO2 available (4.5 mol) is more than the
amount required (0.50 mol), the limiting reactant is
HF.
Worksheet
Limiting Reactant