MOLE RATIOS IN
CHEMICAL
EQUATIONS
STOICHIOMETRY
the study of the
quantitative relationships
that exist in chemical
formulas and reactions
Particle Relationships in a
Balanced Chemical Equation
•
The Haber Process
o N2(g) + 3H2(g) → 2NH3(g)
o 1 molecule of nitrogen + 3 molecules of hydrogen
→ 2 molecules of ammonia
o 10 molecules of nitrogen + 30 molecules of hydrogen
→ 20 molecules of ammonia
Mole Relationships in Chemical
Reactions…
The coefficients in a
balanced equation give the relative
amounts (in moles)
of reactants and products.
The coefficients represent moles…
2NaCl  2Na + Cl2
There are ____ moles of salt.
There are ____ moles of sodium.
There is ____ mole of diatomic Cl.
WHAT IS A MOLE RATIO?
It is the ratio amounts of the entities in a
chemical reaction.
ex. 2H2(g) + O2(g)
2
:
1
2H2O(g)
:
2
Let’s Make Some Smore’s!!!
DETERMINING
AMOUNTS USING
MOLE RATIOS...
Using Ratios to Solve Problems
•
•
•
•
Use known ratio to find out unknown.
o E.g. How many moles of ammonia can be produced from 3.12
moles of hydrogen?
N2(g) + 3H2(g) → 2NH3(g)
Known:
3H2 : 2NH3
Unknown:
3.12 moles H2 : x moles of NH3
Setup Equation:
2NH3/3H2
x NH3
•
= x NH3/3.12H2
= (2NH3)(3.12H2)/3H2
= 2.08 moles of NH3 produced
Mole ratio method can also be used.
EXAMPLE 1: If you start with 50.0g of NaCl, how
many grams of chlorine are produced when the salt
is decomposed?
Step 1: Write a balanced chemical equation.
EXAMPLE 1: If you start with 50.0g of NaCl, how many
grams of chlorine are produced when the salt is
decomposed?
Step 2: Find the number of moles of the given
substance
n = m/ MM
MM(NaCl) = 22.99 g + 35.45g = 58.44g/mol
n = 50.0 g / 58.44 g/mol = 0.8556 moles
Don’t round until the end!!!!!!!!!!!!!!!!!!!
EXAMPLE 1: If you start with 50.0g of NaCl, how many
grams of chlorine are produced when the salt is
decomposed?
Use the balanced equation to find the mole
ratio of given substance to moles of desired
substance
Mole : mole problem
= moles calculated of given x moles of desired
moles of given
0.8556 moles NaCl x 1mole Cl2
2 moles NaCl
= 0.4278 moles of Cl2
EXAMPLE 1: If you start with 50.0g of NaCl, how many
grams of chlorine are produced when the salt is
decomposed?
Convert moles of
desired substance
to whatever quantity(mass,
volume or particles)
is desired
EXAMPLE 2: What amount of oxygen is required
to react completely with 6.4 x 10-2 mol of aluminum
to produce aluminum oxide?
Learning check
1. If you decompose 500.0 g of sodium chloride, how
many grams of sodium are produced? 196.7 g
1. If you react 450.0 g of copper (II) nitrate with excess
2.
calcium, how much copper (II) is produced. 152.5 g
If you combust 250.0 g of nonane,C9H20 how many
liters of oxygen are consumed to make the reaction
go to completion? Assume STP. 611.1 L
• Chalk it up to Molar Relationships Activity
o p301
HOMEWORK:
Mole Ratios and
Stoichiometry
Worksheet
p305 #7 & 8