Transcript Stoichiometry

Start-Up
What is the molar mass for Calcium hydroxide?
A. 57.08 g/mol
B. 74.08 g/mol
C. 64.08 g/mol
D. 27 g/mol
Stoichiometry
Stoichiometry
 The molar relationship between all of the
compounds in a balanced equation.


Law of Conservation of Mass
What is on the left (reactant side) must equal what is on the
right (product side).
Ratio
 What is a molar ratio?
 The ratio is represented by the coefficient in
front of the chemical formula.
 In stoichiometry, a molar ratio is the small,
whole number ratio between each of the
participants in a chemical reaction.
1N2 + 3H2  2NH3
The ratio of Nitrogen to Hydrogen to Ammonia is
1:3:2
Steps for Determining Molar Ratio
 Step 1: Write out the equation.
 Step 2: Balance the equation.
 Step 3: Determine the molar relationships
Example
 Write and balance the equation for the reaction
of Calcium hydroxide and Ammonium sulfate
yields Calcium sulfate and ammonia and water.
 What is the mole ratio between each of the
participants?
The Step-by-Step Process
 Write out the equation.
 Ca(OH)2(aq)+ (NH4)2SO4(aq) → CaSO4 + NH3(g) + H2O(l)
 Balance the Equation
 Ca(OH)2(aq)+ (NH4)2SO4(aq) → CaSO4 + 2NH3(g) + 2H2O(l)
 Determine the molar relationships
 1:1:1:2:2
Another example
 Write and balance the reaction of sodium with water
to yield sodium hydroxide and hydrogen gas.
 What are the ratios?


2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
The ratio is 2:2:2:1
Now try this one
 Write and balance the equation for the reaction of
ammonia with oxygen to yield nitric acid (HNO3)
and water.


NH3(g) + 2O2(g) → HNO3(aq) + H2O(l)
The ratio is 1:2:1:1
The Key
 Stoichiometry means that if you know one piece of
information about ONE compound in an equation,
you can determine EVERYTHING else!!!!!
 If you have 3L of Nitrogen, how many liters of
ammonia will you produce?
N2 + 3H2  2NH3
Think of it as a recipe
 Let’s look at that last reaction again.
 N2(g) + 3H2(g)  2NH3(g)
 If you start out with 1 mole of Nitrogen gas and 3
moles of Hydrogen gas, you will make 2 moles of
Ammonia gas.
 It is important in industry to know the exact
proportions of your ingredients so that you will not
have excess waste in your product.
How many grams of silver chloride can be
produced from the reaction of 17.0 g silver
nitrate with excess sodium chloride solution?
1. Write the balanced equation
17.0g
?g
AgNO3 + NaCl  AgCl + NaNO3
2. Given and asked for
3. Moles of given
17.0g AgNO3 x 1 mol
170 g
=
0.100 mol AgNO3
Mass-Mass Problem Cont.
AgNO3 + NaCl  AgCl + NaNO3
4. Moles asked for
0.100 mols AgNO3 x 1 mol AgCl =
1 mol AgNO3
0.100 mol AgCl
5. Convert your answer
0.100 mol AgCl x 144 g AgCl =
1 mol AgCl
14.4 g AgCl
Example #2
How many grams of calcium hydroxide will
be needed to react completely with 10.0 g of
phosphoric acid (H3PO4) in a double
displacement reaction?
1. Balanced equation
?g
10.0 g
3Ca(OH)2 + 2H3PO4  Ca3(PO4)2 + 6HOH
2. Given & asked for
3. Mols given
10.0 g H3PO4 x 1mol H3PO4 =
98.0 g
0.102 mol H3PO4
4. Mols asked for
0.102 mol H3PO4 x 3 mol Ca(OH)2 =
2 mol H3PO4
0.153 mol Ca(OH)2
5. Convert answer
0.153 mol Ca(OH)2 x 74 g
= 11.3 g Ca(OH)2
1 mol Ca(OH)2
What mass of sodium oxide is produced by the
reaction of 1.44 g of sodium with oxygen?
4Na + O2  2Na2O
1.44g
?g
1.44g x 1mol / 23g = 0.0626mol Na
0.0626mol Na x 2Na2O / 4Na = 0.0313mol Na2O
0.0313mol Na2O x 62g / 1mol = 1.94g Na2O
How many kg of lead (II) nitrate will be needed
to react with sodium chromate to produce 4.62
kg of lead (II) chromate?
Pb(NO3)2 + Na2CrO4  2NaNO3 + PbCrO4
?kg
4620g
(4.62kg)
4620g x 1mol / 323g = 14.3mol PbCrO4
14.3mol PbCrO4 x 1mol / 1mol = 14.3mol Pb(NO3)2
14.3mol Pb(NO3)2 x 331g / 1mol = 4730g (4.73kg)
Pb(NO3)2
What quantity of hydrogen gas is formed when 0.85 g of
lithium reacts with water? How much lithium hydroxide
is produced?
2Li + 2H2O  2LiOH + H2
0.85g
?g
0.85g Li x 1mol / 7g = 0.12mol Li
0.12mol Li x 1H2 / 2Li = 0.060mol H2
0.060mol H2 x 2g / 1mol = 0.12g H2
3.0g LiOH
What mass of water is given off when 192 kg of
C7H14 burn completely in air? How much oxygen
is used?
2C7H14 + 21O2  14CO2 + 14H2O
192,000g (192kg)
?g
192,000g C7H14 x 1mol / 98g = 1960mol C7H14
1960mol C7H14 x 14mol / 2mol = 13700mol H2O
13700mol H2Ox 18g / 1mol = 247,000g H2O
658,000g O2
Classwork
 P. 307, #1-4
 Fe2O3 + 2Al  2Fe + Al2O3
 P. 309, #1-4
Homework
 P. 311, #1-7