from yesterday's demo:
ex. Haber process
N2 + 3H2  2NH3
recall mole ratio: the relationship between moles in a chemical equation, shown by the
coefficients of a balanced chemical equation
in this case for reactant 1:3 nitrogen gas to hydrogen gas
let's say I have stoichiometric amounts of each reactant, how much of the products
would I produce?
2 moles of nitrogen gas and unlimited H2?
what would happen if we had 2 moles of nitrogen gas, but only 3 mole of hydrogen
gas?
- in nature you usually don't have stoichiometric amounts of reactants,
ex. cellular respiration
C6H12O6 (s) + 6 O2 (g)  6 CO2 (g) + 6 H2O (l)
- what do you think will be most likely to stop this reaction from happening?
LIMITING AND EXCESS REAGENTS
limiting reagent
- reactant that is completely used up in the reaction
- determines how much product will be produced
excess reagent
- reactant that remains after the reaction is over
ex. If 13.7 g of butane, C4H10 is combusted in 14.2 g of oxygen gas to produce
carbon dioxide and water find:
a.
b.
c.
d.
the limiting reagent
the mass of carbon dioxide produced
the mass of water produced.
the mass of excess reagent which remains unreacted
- write balanced chem. equation
2 C4H10(g) + 13 O2(g)
8 CO2(g) + 10 H2O(l)
- write mole ratio
- convert masses to moles
- calculate amount of product produced for both butane and O2
- whatever is lower is your limiting reagent
balanced rxn 2 C4H10
13 O2
8 CO2
10 H2O
mole ratio
2
13
8
10
mass (g)
13.7
14.2
M (g/mol)
sldkfjsdofk
32.00
n (mol)
ex. In the textile industry, chlorine gas is used to bleach fabrics. Any
of the toxic chlorine that remains after the bleaching process is
destroyed by reacting it with a sodium thiosulphate solution:
Na2S2O3 (aq) + 4 Cl2 (g) +
5
H2O (l)  2 NaHSO4 (aq) + 8 HCl (aq)
If 135 kg of sodium thiosuphate reacts with 50.0 kg of Cl2 and 238 kg of water how
many grams of sodium bisulphate are expected?
balanced rxn
mole ratio
mass (g)
M (g/mol)
n (mol)
Limiting Reagent: S'mores Lab
S'mores are a Canadian camping delicacy – a treat made over an open
fire at the end of an exhausting day spent hiking, canoeing, and generally having
way way too much fun without a TV around. Today, we will use a microwave to
make s'mores.
The balanced reaction for making s'mores is as follows:
2 Gc + 3 Cc + 1 Mm  1 S'more
where Gc is a Graham cracker, Cc is a chocolate chip, and Mm is a marshmallow.
1. Using your reagents (provided by the teacher), and the balanced S'mores reaction,
calculate whether you have too few Gc or Mm to carry out a reaction that will give you 2
S'mores. Cc is your excess reagent.
Gc
from balanced equation, what is your
mole ratio?
how many moles of each reactant do
you have?
how many moles of each reactant do
you need to make 2 mol of S'mores?
Cc
Mm
S'more
excess
excess
2
2. What are you missing? How many? This is your limiting reagent.
limiting reagent:
excess reagent:
3. Using this lab and your textbook, define excess and limiting reagents (pp.187-188).
excess reagent:
limiting reagent:
4. Once the above questions are completed bring this sheet to the teacher to obtain enough
Gc or Mm to produce 2 S'mores. Bon appetit! 
*by Bogna Haddad, adapted from Donna, Dept. of Science, Notre Dame High School.
portfolio:
LIMITING REAGENTS
1. If 3.85 g of concentrated sulphuric acid and 2.927 g of sodium chloride are mixed to
produce sodium sulphate and hydrochloric acid find:
H2SO4 + 2 NaCl
a.
b.
c.
d.
the
the
the
the
Na2SO4 + 2 HCl
limiting reactant.
mass of hydrogen chloride produced
mass of sodium sulphate produced.
mass of excess reagent which remains unreacted. (Ans. 1.39 g)
2. If 4.57 g of hydrochloric acid is added to 5.45 g of zinc to produce zinc chloride and
hydrogen gas find:
Zn(s) + 2 HCl(aq)
a.
b.
c.
d.
the
the
the
the
ZnCl2(aq) + H2(g)
limiting reactant.
mass of hydrogen gas produced
mass of zinc chloride produced.
mass of excess reagent which remains unreacted. (Ans. 1.35 g)
3. If 27.2 g of gaseous ammonia is passed over 135.6 g of heated copper(II) oxide to
produce nitrogen, copper and water vapour find:
2 NH3(g) + 3CuO(s)
a.
b.
c.
d.
e.
the
the
the
the
the
N2(g) + 3Cu(s) + 3 H2O(g)
limiting reactant.
mass of nitrogen formed
mass of copper formed.
mass of water formed
mass of excess reagent which remains unreacted. (Ans. 7.85 g)