Transcript Stoichiometry - Brookwood High School

Stoichiometry
Section 12.1
What is Stoichiometry?
Study of quantitative relationships between amounts of
reactants used and products formed.
Based on the Law of Conservation of Mass (Mass of the
Reactants = Mass of the Products)
Ex. 4 Fe (s) + 3 O 2 (g)  2 Fe2O3 (s)
Mole – Mass Relationships
Coefficients in a balanced equation can be interpreted in
terms of representative particles and also by numbers of
moles of particles.
We can also use what we know about the conversion factor
that relates mass and number of moles to find the mass of
either the reactants or products.
Mole – Mass Relationships
Ex. 4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
4 mol Fe x 55.85 g Fe = 223.4 g Fe
1 mol Fe
3 mol O2 x 32.00 g O2 = 96.0 g O2
1 mol O2
Mass of Reactants
= 319.4 g
2 mol Fe2O3 x 158.7 g Fe203 = 319.4 g
1 mol Fe203
Mass of Products
= 319.4 g
Mole Ratios
Ratio between the numbers of moles of any two substances
in a balanced chemical equation.
Ex. 2 Al (s) + 3 Br2 (l)  2 AlBr3 (s)
2 mol Al and _2 mol Al_
3 mol Br2
2 mol AlBr3
3 mol Br2 and _3 mol Br2_
2 mol Al
2 mol AlBr3
2 mol AlBr3 and 2 mol AlBr3
2 mol Al
3 mol Br2
Mole Ratio Practice
What mole ratios can be written for the decomposition of
potassium chlorate?
Answer:
2 KClO3 (s)  2 KCl (s) + 3 O2 (g)
2 mol KClO3 and 2 mol KClO3
2 mol KCl
3 mol O2
_2 mol KCl_ and _2 mol KCl_
2 mol KClO3
3 mol O2
__3
mol O2_ and _3 mol O2
2 mol KClO3
2 mol KCl
Mole – Mole Conversions
1. All stoichiometric calculations begin with a balanced
equation.
2. Mole ratios based on the balanced chemical equation are
also needed.
3. A limiting reactant is a reactant that limits the extent of the
reaction and determines the amount of product. This is
the reactant you have the least amount of.
Calculation:
Moles of known x moles of unknown = moles of unknown
moles of known
Mole – Mole Conversion Practice
2 K (s) + 2 H2O (l)  2 KOH (aq) + H2 (g)
How can you determine the number of moles of hydrogen produced
when .0400 mole of potassium is used?
1. Write the balanced equation
2. Given
= .0400 mole K
Unknown = moles of H2
3. Write the mole ratio:
1 mole H2
2 mole K
4. Convert using: moles of known x moles of unknown
moles of known
Answer: .0400 x 1 mole H2 = .0200 mol H2
2 moles K
Mole – Mole Relationships in
Equations
1. Balance the equation.
2. Coefficients = number of moles of each substance.
3. Use “x” for the “how many” compound.
4. Use ratio of moles given in problem to actual moles in
equation.
5. Set up ratio.
6. Solve.
Mole – Mole Relationships in
Equations Example
Example:
_6__
__x_
2 H2 + O2  H2O
How many moles of water can be produced with 6 moles of
hydrogen?
1. Equation is balanced.
2. There are 2 moles of hydrogen, 1 mole oxygen, and 2
moles water.
3. 6 H2 = x H2O
6 = x and 2x = 12
2 H2
2 H2O
2 2
x=6
4. X = 6 moles water
Stoichiometry Practice I
(Mole-Mole Conversions)
1.
2.
3.
4.
5.
2 H2 + O2  2 H2O
How many moles of water can be produced with 6 moles
of hydrogen?
How many moles of oxygen would be required to fully
react with 8 moles of hydrogen?
How many moles of water can be produced with 4 moles
of oxygen?
How many moles of hydrogen would be required to
produced 10 moles of water?
How many moles of oxygen would be needed to produce
20 moles of water?
Mole to Mass Relationships in
Equations
Balance the equation.
2.
Coefficients = # of moles of each substance.
3.
Use “x” for the “how many” compound.
4.
Use ratio of moles given in problem to actual
moles in equation.
5.
Set up ratio and solve for “x”.
6.
Multiply your answer by the molar mass of
the element or compound you are trying to
find.
(Example: Stoichiometry Practice II, # 4)
1.
Mass to Mass Relationships in
Equations
Balance the equation.
2. Find the molar mass of each of the
reactants and products in the equation.
3. Use “x” for the “how many” compound.
4. Use ratio of mass given in problem to
actual mass in equation.
5. Set up the ratio and solve for “x”.
(Example: Stoichiometry Practice II, # 6)
1.