Download Limiting reactant - Dr. Gregory Chemistry

Measuring
Matter
Moles and Avogadro’s Number
The Mole
› A mole (mol) a measure of the amount of a
substance.
› The value of a mole is 6.02 x 1023 particles.
This is also called Avogadro’s number.
› Particles can be atoms, molecules, ions,
formula units.
› Equality: 1 mole = 6.02 x 1023 particles
Conversion Factors
›Each equality can be written as 2
conversion factors.
›Equality: 1 mole = 6.02 x 1023 particles
›Conversion factors:
1 𝑚𝑜𝑙𝑒
6.02 𝑥 1023 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
and
6.02 𝑥 1023 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
1 𝑚𝑜𝑙𝑒
Converting Between Particles and
Moles
›A sample contains 8.3 x 1024 atoms of
silver. How many moles is this?
The Mass of a Mole
› Molar mass is the mass (in grams) of one
mole of substance. This is the mass on the
periodic table.
› Example. 1 mole of carbon atoms:
1 𝑚𝑜𝑙𝑒 𝐶 𝑎𝑡𝑜𝑚𝑠 = 12.01 𝑔 𝐶
Conversion factors:
1 𝑚𝑜𝑙𝑒 𝐶 𝑎𝑡𝑜𝑚𝑠
12.01 𝑔 𝐶
and
12.01 𝑔 𝐶
1 𝑚𝑜𝑙𝑒 𝐶 𝑎𝑡𝑜𝑚𝑠
The Mass of a Mole
› If the substance is a molecule or ionic
compound, the molar mass of the compound
must be calculated.
Example: What mass of CH4 (methane) is
contained in 8.12 moles of methane?
Converting Between Grams and
Moles
›A chunk of aluminum has a mass of 274
grams. How many moles of aluminum
are in the sample?
Converting Between Grams and
Moles
›What mass of methane (CH4) is contained
in 7.51 x 1025 molecules of methane?
Converting Between Grams and
Moles
›How many molecules of oxygen are
contained in a 214 grams sample of
water?
Calculating Empirical Formula
given % composition
›Steps
1. Change % to grams
2. Convert grams to moles
3. Divide all moles by the smallest mole
4. Write empirical formula
Calculating Empirical Formula
given % composition
›Practice
Calculating Molecular Formula
given Molecular Mass
›Steps
Constant =
𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
𝐸𝑚𝑝𝑖𝑟𝑖𝑐𝑎𝑙 𝑚𝑎𝑠𝑠
(Empirical formula)constant = molecular formula
Calculating Molecular Formula
given Molecular Mass
›Practice
Stoichiometry
Stoichiometry is the study of quantitative
relationships between the amounts of
reactants used and amounts of products
formed in a chemical reaction. It is based on
the law of conservation of mass.
Stoichiometry
Stoichiometric ratios can be used to
determine how much product will form or
how much reactant will be used in a chemical
reaction.
Using Stoichiometry
Stoichiometric ratios can be formed for
chemical reactions as shown below.
4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
4 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒
3 𝑚𝑜𝑙𝑒𝑠 𝑂2
or
4 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒
2 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒2𝑂3
or
3 𝑚𝑜𝑙𝑒𝑠 𝑂2
2 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒2𝑂3
Using Stoichiometry
How many moles of CO2 are produced
when 20.0 moles of C3H8 are burned?
C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
Using Stoichiometry
How many moles of O2 are needed to
completely react with 10.0 moles of C3H8?
C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
Using Stoichiometry
How many moles of H2O are produced
when 95.0 g of C3H8 are burned?
C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
Using Stoichiometry
How many grams of CO2 are produced
when 73.0 g of C3H8 are burned?
C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
Limiting Reactant
Limiting reactant is the reactant that
“runs out” in a chemical reaction; it also
determines the amount of product formed.
Reactant left over at the end of a chemical
reaction is called the excess reactant.
The amount of product formed when the
limiting reactant is used up is called theoretical
yield.
Determining Limiting Reactant
If 200.0 g sulfur reacts with 100.0 g
chlorine, what is the limiting reactant?
S8(l) + 4 Cl2(g)  4 S2Cl2(l)