Transcript Stoichiometry

October 11, 2011
 Stoichiometry:
 Balanced
math of chemical reactions
equations tell us a lot of
information
N2 (g)
+
3H2 (g)

2NH3 (g)

+
2 atoms N
+
6 atoms H

2 atoms N and 6
atoms H
1 molecule N2
+
3 molecules H2

2 molecules NH3
10 molecules N2
+
30 molecules H2

20 molecules NH3
1 x (6.02x1023
molecules N2)
+
3 x (6.02x1023
molecules H2)

2 x (6.02x1023
molecules NH3)
moles
1 mole N2
+
3 moles H2

2 moles NH3
mass
28g N2
+
3 X 2g H2

2 x 17g NH3
+
34 g reactants

34 g products
+
3 x (22.4 L) H2
67.2 L

2 x (22.4 L) NH3
44.8 L
particles
volume at stp
22.4 L N2
22.4 L
 Hydrogen
sulfide is found in volcanic areas.
The balanced equation is
2H2S (g) + 3O2 (g)  2SO2 (g) + 2H2O (g)
 Find

the number of representative particles
2 molecules H2S + 3 molecules O2 
2 molecules SO2 + 2 molecules H2O
 Hydrogen
sulfide is found in volcanic areas.
The balanced equation is
2H2S (g) + 3O2 (g)  2SO2 (g) + 2H2O (g)
 Find

the number of moles
2 moles H2S + 3 moles O2 
2 moles SO2 + 2 moles H2O
 Hydrogen
sulfide is found in volcanic areas.
The balanced equation is
2H2S (g) + 3O2 (g)  2SO2 (g) + 2H2O (g)

Find the masses of the reactants and products

Use the atomic masses on the periodic table!

2(2x1 + 32)g+ 3 (2x16)g  2(32 + 2x16)g+ 2(2x1 + 16)g
2(34)g + 3(32)g  2(64)g + 2(18)g
128g  128g
N2 + 3H2  2NH3
Mole ratios…
1 mole N2
3 moles H2
2 moles NH3
3 moles H2
3 moles H2
1 moles N2
3 moles H2
2 moles NH3
1 mole N2
2 moles NH3
2 moles NH3
3 moles H2
N2 + 3H2  2NH3
 How
many moles of ammonia are produced
when 0.5 moles of nitrogen react with
hydrogen?
 How
many moles of nitrogen will react with
7.0 moles of hydrogen gas?
N2 + 3H2  2NH3
 If
56 g N2 reacts with excess hydrogen, how
much ammonia is produced?

excess = extra
N2 + 3H2  2NH3
 If
56 g N2 reacts with excess hydrogen, how
much ammonia is produced?
 Assuming
STP, how many liters of oxygen are
required to produce 19.8 L SO3?
2SO2 + O2  2SO3
 Assuming
STP, how many liters of SO3 can be
produced when 48 grams O2 react with
excess SO2?
2SO2 + O2  2SO3
 Tin
(II) fluoride used to be a common
ingredient in toothpaste. It is formed with
this reaction: Sn + HF  SnF2 + H2


Balance the equation
Sn + 2HF  SnF2 + H2
How many grams of SnF2 can be produced by reacting
7.22 x 1023 molecules of HF with excess tin?
 Why

do we balance equations?
Law of Conservation of Matter
 What



is conserved during a reaction?
Atoms
Mass
NOT necessarily moles
 We
can use the balanced equation to
determine limiting reagent

How many complete cars can be produced from
eight car bodies and 48 tires?

How many complete cars can be produced from
12 car bodies and 36 tires? What is the limiting
reagent? What is in excess?
36 tires/4 tires per car = 9 complete cars
 Tires are the limiting reagent; car bodies are excess

2Cu + S(s)  Cu2S
What is the limiting reagent when 80.0 grams copper react
with 25.0 grams sulfur?
What is the maximum number of grams of Cu2S that can be
formed?