SOLVE: 1.5e24 molecules of
SO2 = ____ grams of SO2?
S2 + 2O2  2SO2
And how many moles of S2?
Day 4 10-22
Limiting Reactants
Limiting Reactant – 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 one you
will run out of
Excess Reactant – any substance that is not
used up completely in a reaction – left over
Limiting Reactants
To determine the Limiting Reactant – use
either reactant to calculate the amounts
necessary for reaction
Example:
4NH3(g) + 6NO(g)
5N2(g) + 6H2O(l)
Given the following, determine the limiting reactant:
40 g NH3
41 g NO
Limiting Reactants
Example:
4NH3(g) + 6NO(g)
5N2(g) + 6H2O(l)
Given the following, determine the limiting reactant:
40 g NH3
41 g NO
Limiting Reactants
2Na + Cl2 → 2NaCl
Start with 4 moles of Na and 3 moles
of Cl2:
limiting = ?
excess = ?
Limiting Reactants
2Na + Cl2 → 2NaCl
Start with 26 grams of Na and 35.5
grams of Cl2:
limiting = ?
excess = ?
1. If you start with 2.5 moles of
solid aluminum and allow it to
react with 2.5 moles of CuCl2
which reactant will be left over
at the end?
2. Why is today Mole Day?
Day 5 10-23
1. Which reactant determines your
theoretical yield?
Day 6 10-24
Percent Yield
Percent Yield =
Actual Yield
X 100
Theoretical Yield
 the percent yield is a measure of the
efficiency of a reaction carried out in
the lab.
- a perfect percent yield would
be a 100%
Example # 1:
Calcium carbonate, which is found in seashells, is
decomposed by heating. The reaction is below:
CaCO3(s)  CaO(s) + CO2(g)
What is the theoretical yield of CaO if 24.8
grams of CaCO3 is heated?
If only 12 grams of CaO are recovered, what
is the percent yield? Percent Yield = Actual Yield X 100
Theoretical Yield
What could be the cause?
Quarterly Practice
A solution containing 3.50 g sodium phosphate is mixed
with a solution containing 6.40 g barium nitrate. After
the reaction is complete, 4.85 g barium phosphate are
collected.
1. What is the limiting reagent?
2. What is the theoretical yield of barium phosphate?
3. What is the percent yield of barium phosphate?
2Na3PO4(aq) + 3Ba(NO3)2(aq)  6NaNO3(aq) + Ba3(PO4)2(s)
molar masses:
Na3PO4 = 163.9
Ba(NO3)2 = 261.3
Ba3(PO4)2 = 601.9
12
Quarterly Practice
A solution containing 3.50 g sodium phosphate is mixed
with a solution containing 6.40 g barium nitrate. After
the reaction is complete, 4.85 g barium phosphate are
collected.
1. What is the limiting reagent?
2. What is the theoretical yield of barium phosphate?
3. What is the percent yield of barium phosphate?
2Na3PO4(aq) + 3Ba(NO3)2(aq)  6NaNO3(aq) + Ba3(PO4)2(s)
If you start with 3.50 g Na3PO4 you NEED 8.37 g Ba(NO3)2
So Barium nitrate is limiting and you start your theoretical
with 6.40 g barium nitrate
Theoretical yield = 4.91
13
% yield = 98.8 %
Assignment
Review sections 12.1 and 12.2 and
complete # 8 on page 389, # 11 on page
391, # 13 on page 393, and # 23 on page
398 – due tomorrow
Get to # 11
Hand in assignment
from Friday
Assignment
Review sections 12.1 and 12.2 and
complete #s 5, 6, 8, 9, and 10 on page
389, #s 11 and 12 on page 391, and #s
13 and 14 on page 393 – due beginning
of class Tuesday 10-29
Complete #s 21-25 on page 398 – due
Wednesday 10-30