Transcript Chemistry Chapter 11: Stoichiometry

Chemistry Chapter 11:
Stoichiometry
•Stoichiometry is the use of balanced equations
to calculate chemical quantities.
•Always balance every equation you deal with in
stoichiometry.
•You will need to be able to translate chemical
equations in terms of mass, particles, moles,
and volume (for gases only).
•There are 3 quantities conserved in every
chemical equation: atoms, mass, and energy.
Representative Particles
• The representative particle of most
elements is the atom.
• The representative particle of molecular
compounds, and the diatomic elements, is
the molecule.
• The representative particle of ionic
compounds is the formula unit.
Translating Chemical Equations
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4Fe(s) + 3O2(s)  2Fe2O3(s)
Translate this chemical equation in terms of :
A) Moles
B) Mass
C) Representative particles
Translate the following equation in terms of
volume:
• 2H2(g) + O2(g)  2H2O(g)
Conversion Factors in
Stoichiometry
• Conversion Factors in stoichiometry come
from a balanced equation.
• 4Fe(s) + 3O2(s)  2Fe2O3(s)
• 4 mole Fe
3 moles O2
4 mole Fe
2Fe2O3(s)
• You can also flip both of these conversion
factors to get a new conversion factor.
Mole/Mole Problems
• 4Fe(s) + 3O2(s)  2Fe2O3(s)
• Using the balanced equation above, you
can determine mole quantities:
• Try this…given 8.5 moles of solid iron, and
excess oxygen gas, how many moles of
solid iron(III) oxide can be produced?
Steps to Stoichiometric Problems
1. Always start with a correctly written skeleton or
balanced equation and balance the equation.
2. Write the unknown and known.
3. Looking at the unknown and known, translate the
equation with the required units and write those units
above the mole amount if the units are not mole.
4. Write 2 blanks, with a x between them and a third
blank after an =.
5. Write your known # and units over 1 in the 1st blank.
6. Drag your known units to the second denominator.
7. Write your unknown units in the last 2 numerators.
8. Fill in the numbers in blank 2 from your balanced
equation…then solve using a calculator.
Problems With Mass, Particles, or
Volume
• In stoichiometry problems with other
quantities like mass, particles, or volume,
you do the same steps but translate the
balanced equation in the form you need.
• All problems in this chapter are 2-step
problems.
• Try this…How many grams of solid iron(III)
oxide are produced if 133.4 L of oxygen
gas are reacted with excess solid iron?