reaction stoichiometry. deals with the mass relationships that exist between reactants and product...
TRANSCRIPT
Deals with the mass relationships that exist
between reactants and product
In this type of chemistry, a quantity is given, and based on the chemical formula, a calculation of an unknown is completed.
Problem types fall into four different categories
Reaction Stoichiometry
A given amount in moles and an
unknown amount in mole
Mole known → mole unknown
Reaction Stoichiometry
A given amount in moles and an
unknown amount in grams
Mole known → mole unknown → gram unknown
Reaction Stoichiometry
A given amount in grams and an
unknown amount in moles
Gram known → mole known → mole unknown
Reaction Stoichiometry
A given amount in grams and an
unknown amount in grams
Gram known → mole known → mole unknown → gram unknown
Reaction Stoichiometry
The conversion factor used to relate the
number of grams of a substance to the number of moles of the substance
Always derived from the periodic table
Example: 101.96 g Al2O3 or 1Mole Al2O3 1 Mole Al2O3
101.96 g Al2O3
Molar Mass
When chemists discover new compounds in the
laboratory they need to be able to determine the chemical formula of the compound in order to replicate it.
They first discover the simplest whole number ratio of atoms in the compound This is known as the empirical formula
From this they derive the actual formula of the compound This is known as the molecular formula
Determining Chemical Formulas
This can be derived knowing either the
percent of each element in a compound or the number of grams used of each element.
Percent to Mass Mass to Mole Divide by Small Multiply till Whole
Determining the Empirical Formula
A compound consists of 25.94% N and 74.06
% O; what is its empirical formula?
Determining the Empirical Formula
A white solid consists of Na, S, and O. 32.4% is
Na, and 22.6% is S, what is the compounds empirical formula?
Determining the Empirical Formula
A scientist formed a compound out of only tin
and chlorine and it weighed 2.57 g. He knew he used 1.17 g of tin. Can you help him find the empirical formula?
Determining the Empirical Formula
Any multiple of a compounds empirical
formula may or may not be a correct molecular formula.
For example C2H4 and C3H6 both have the same ratio of Carbon to Hydrogen (3:1), however, the substances are completely different.
Molecular Formula
By dividing the molecular mass by the mass
of the empirical formula, we can obtain the multiple by which the molecular formula can be found.
Calculating Molecular Formulas
A compound has an empirical formula of CH2O
and a molar mass of 180 g / mol, what is the molecular formula of the compound?
Finding Molecular Formulas
A compound has an empirical formula of NO2
and a molar mass of 92.02 g/mol. What is its molecular formula?
Finding Molecular Formulas
A compound contains 0.70 g Cr, 0.65 g S, and
1.30 g O, the molar mass of the molecule is 392.2 g/mol. What is the molecular formula?
Practice: do 39 p 237, and 158 p. 929
Finding Molecular Formulas
A conversion factor that relates any two
substances in a chemical reaction
This information comes directly from the balanced chemical equation
Mole Ratio
Ideal = all of the reactants are converted into
products and we are not concerned about any other reactants left over
Usually the question will say one of the reactant is in excess
Ideal Stoichiometry
How many moles of H2O will be produced by
the reaction of 10 grams of H2 reacting with excess O2?
Stoichiometry
How many moles of NH3 will be produced from
3.8 moles of N2 reacting with excess H2 according to the following equation:
N2 + 3H2 → 2NH3
Stoichiometry
N2 + 3H2 → 2NH3
Using the same equation starting with 15.9 grams of nitrogen, how many moles of H2 are required to completely react with the N2?
Stoichiometry
The limiting reactant is the reactant that limits
the amount of the other reactant and the amount of product that can form in a chemical reaction.
Limiting Reactants
C + O2 → CO2
1 mole of Carbon reacts with 1 mole of O2 to yield 1 mole of CO2
or5 mole of Carbon reacts with 5 mole of O2 to yield 5 mole of CO2
But what if you started with 5 moles of Carbon and 10 moles of O2?
Limiting Reactant
C + O2 → CO2
The 5 moles of Carbon with react with the first 5 moles of O2 to yield 5 moles of CO2….but 5 moles of O2 would be left over.
If there was more Carbon to start with, more CO2 could have been formed.
Carbon in this case is a limiting reactant.
Limiting Reactant
N2H4 + 2H2O2 → N2 + 4H2O
If 0.75 moles of N2H4 is mixed with 0.50 moles of H2O2, what is the limiting reactant?
How much of the excess reactant remains unchanged?
How much of each product is formed, in moles?
Limiting Reactant
Carbon reacts with steam to produce hydrogen and carbon monoxide. a. Write a balanced chemical equation for the
reaction.
b. If 2.40 moles of Carbon are exposed to 3.10 moles of steam, identify the limiting reactant.
c. How many moles of each product are formed?
d. What mass of each product is formed?
3Fe + 4H2O → Fe3O4 + 4H2
a. When 36.0g of H2O is mixed with 167g of Fe, which is the limiting reactant?
b. What is the mass, in grams, of the Iron Oxide produced?
c. What is the mass, in grams, of the excess reactant that remains when the reaction is completed?
The theoretical yield is the maximum amount
of product that can be produced from a given amount of reactant.
The measured amount of product obtained from a reaction is called the actual yield of that product.
Percent Yield
In most reactions, the actual product is less
than the theoretical product.
This is due to side reactions or impurities in the product which must be removed.
Percent Yield
The percent yield is the ratio of the actual
yield to the theoretical yield, multiplied by 100.
Percent Yield