Transcript Stoichiometry

Stoichiometry
What does a chemical equation really
mean?
Coefficients tell us
• Atoms or molecules
• Mols
• Liters
Avogadro’s number – 6.022 x
23
10
Based on Amedeo Avagadro’s 1811 proposal
that the volume of a gas (at a given
pressure and temperature) is proportional
to the number of atoms or molecules
regardless of the nature of the gas.
What is stoichiometry?
Composition stoich – deals with mass relationships
of elements in compounds
Reaction stoich – deals with relationships between
reactants and products
Mole Ratios
Conversion factor relating amount
of moles of any two substances
Example: decomposition of aluminum oxide
2Al O (l)  4Al(s)  3O (g)
2
3
2
2 mol Al 2O3
4 mol Al
or
4 mol Al
2 mol Al 2O3
2 mol Al 2O3
3 mol O2
or
3 mol O2
2 mol Al 2O3
3 mol O2 4 mol Al
or
4 mol Al 3 mol O2
Molar Mass Ratios
Al2O3 – 101.96 g/mol
101.96 g Al 2O3
1 mol Al 2O3
or
1 mol Al 2O3
101.96 g Al 2O3
Al – 26.98 g/mol
26.98g Al
1 mol Al
or
1 mol Al
26.98 g Al
O2 – 32.00 g/mol
32.00 g O2
1 mol O2
or
1 mol O2
32.00 g O2
MUST HAVE…
• Correct molecular formulas
• Balanced chemical equation
Reaction Stoichiometry
4 types of problems
Type 1
• Given and unknown quantities in moles
Amount of given (in mol)  Amount of unknown (in mol)
Type 2
• Given amount is in moles and unknown is mass in grams
Amount given (in mol) 
amount unknown (in mol) 
mass unknown (in g)
Type 3
• Given is amount in grams and unknown is amount in
moles
mass given (in g) 
amount given (in mol) 
amount unknown (in mol)
Type 4
• Given is mass in grams and unknown is mass in
grams
mass given (in g) 
amount given (in mol) 
amount unknown (in mol) 
mass unknown (in g)
Stoichiometric Calculations: Type 1
(mol-mol)
Example 1: The combustion of 2.19 mol
propane (C3H8) produces how much
carbon dioxide?
Example 2: 41.8 mol lithium hydroxide is
combined with carbon dioxide to produce
lithium carbonate and liquid water. How
many moles of water are produced?
Stoichiometric Calculations: Type 2
(mass-mol)
NaHCO3 and Mg(OH)2 are both used as antacids – which is more
effective per gram?
Example 3: 1.00 g NaHCO3 reacts with hydrochloric acid to produce
sodium chloride, water, and carbon dioxide
Example 4: 1.00 g Mg(OH)2 reacts with hydrochloric acid to produce
magnesium chloride and water
Stoichiometric Calculations Type 3
(mol-mass)
In photosynthesis, plants use energy from
the sun to produce glucose C6H12O6,
and oxygen from the reaction of carbon
dioxide and water. What mass, in
grams, of glucose is produced when
3.00 mol of water react with carbon
dioxide?
Stoichiometric Calculations Type 3
(mol-mass)
What mass of carbon dioxide, in grams, is
needed to react with 3.50 mol of water
in the photosynthetic reaction?
Stoichiometry Calculations Type 4
(mass-mass)
Tin (II) fluoride is used in some toothpastes.
It is made by the reaction of tin with
hydrogen fluoride according to the
following equation.
Sn(s) + 2HF  SnF2(s) + H2(g)
How many grams of SnF2 are produced
from the reaction of 30.00 g of HF with
Sn?
Limiting
Reactants
Objectives:
1. Recognize the limiting
reactant
2. Use the limiting reactant
What is a “limiting reactant”?
The substance that is completely used up
first in a chemical reaction
How do I find the limiting reactant?
1.
2.
3.
4.
5.
Analyze the question
Identify the given information
Write a balanced chemical reaction
Convert given information of Reactant 1 to Product A
Convert given information of Reactant 2 to Product A
Theoretical Yield
The amount of product found this way is called the
THEORETICAL YIELD
This is how much could possibly be made if the limiting
reactant was totally consumed
Actual Yield
The amount of product actually obtained in
the laboratory
Percent Yield
Actual Yield
 100%  Percent Yield
Theoretical Yield