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• 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 4 mole Fe

3 moles O2 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 Problems1. 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?