Stoichiometry: Calculations with Chemical Formulas and Chemical Equations

1
Chapter 3

• Stoichiometry Calculations with Chemical
  Formulas and Chemical Equations

2
What is Stoichiometry

• Quantitative nature of chemical formulas and
  chemical reactions.

3
Law of Conservation of Mass

• The total mass of all substances present after a
  chemical reaction is the same as the total mass
  before the reaction.
• Atoms are neither created nor destroyed during
  any chemical reaction.

4
Chemical Equations

• Reactants ? Products
• Reactants
• Products

5
Types of Reactions

• Combination or Synthesis
• Decomposition
• Single Replacement
• Double Replacement
• Combustion

6
Decomposition Reactions

• Rule 1 Metallic chlorates decompose into
• Rule 2 Metallic hydroxides decompose into
• Rule 3 Metallic carbonates decompose into
• Rule 4 Binary compounds decompose into

7
Synthesis Reactions

• Know your decomposition rules, only in reverse.

8
Combustion Reactions

• Excess supply of oxygen will result in the
  production of
• Limited supply of oxygen will result in the
  production of

9
Single Replacement Reaction

• The single element must be more reactive than the
  element it is replacing.

10
Atomic Mass Unit

• Average atomic mass of each element is also known
  as its atomic weight.
• Formula weight sum of the atomic weights of
  each atom in the chemical formula.

11
Mole

• mol
• Unit dealing with atoms, ions, and molecules.
• Avogadros Number
• amu of a compound 1 mole
• Avogadros Number 1 mole

12
amu 1 mole 6.02 x 1023 (atoms, ions,
molecules)

• Calculate the number of carbon atoms in 0.350 mol
  of C6H12O6
• 1. Change given to molecules of the given.
• 2. Change molecules of the given to individual
  atoms of carbon.

13
How many oxygen atoms are in 0.25 mol Ca(NO3)2?

• 9.0 x 1023 atoms

14
Molar Mass

• The mass in grams of 1 mole of a substance is
  called its molar mass.
• Equal to the formula weight.

15
What is the mass in grams of 1 mole of glucose?

• C6H12O6
• Carbon 6 atoms x 12.01 72.06
• Hydrogen 12 atoms x 1.01 12.12
• Oxygen 6 atoms x 16.00 96.00
• Total 180.2

16

• amu 1 mole 6.02 x 1023 mlc, atoms, or ions

17
Calculate the number of moles of glucose in 5.380
grams of this substance.

• Change grams to moles.

18
Determine the number of molecules in 2.35 grams
of glucose.

• Change grams to moles.
• Change moles to molecules.

19
Combustion Analysis

• If you know the amount of carbon dioxide and
  water produced in a complete combustion reaction,
  you can determine the hydrocarbon compound that
  underwent the combustion reaction.

20
The combustion of 0.255 g isopropyl alcohol,
containing C, H, and O, produces 0.561 g CO2 and
0.306 g H2O. Determine the formula for isopropyl
alcohol.

• 1. Change grams of carbon dioxide to moles of
  carbon.

21

• 2. Change grams of water to moles of hydrogen.

22

• Change moles of each to grams of each.

23
Now calculate the mass of oxygen.

• Total mass of sample 0.255 g
• Total mass mass of hydrogen mass of carbon
  mass of oxygen
• 0.255 g 0.154 g C 0.0343 g H 0.067 g Oxygen

24

• Change grams of oxygen to moles of oxygen.

25
Compare the number of moles of each element in
the sample. Divide by the lowest.

• 0.0128 mol C 0.0340 mol H 0.0042 mol O
• Divide by 0.0042
• Ratio becomes 3 8 1
• Formula for Isopropyl alcohol C3H8O

26
Quantitative analysis using chemical equations.
27
How many grams of water are produced in the
complete combustion of 1.5 grams of methane.

• 1. Write a balanced equation.
• CH4 2O2 ? 2H2O CO2

28

• 2. Set up the given.
• 3. Change grams of given to moles of given.
• 4. Mole to mole conversion.
• 5. Change moles of what you are looking for to
  grams.

29
CH4 2O2 ? 2H2O CO2
30

• Solid lithium hydroxide is used in space vehicles
  to remove exhaled carbon dioxide. The lithium
  hydroxide reacts with gaseous carbon dioxide to
  form solid lithium carbonate and liquid water.
  How many grams of carbon dioxide can be absorbed
  by each 1.00 grams of lithium hydroxide.
• 1. Write a balanced equation.
• 2. Set up the problem.
• 3. Solve for the unknown.

31
Limiting Reactants

• One of the reactants is used up before the other.
• The reactant that is used up/completely consumed
  in the reaction is the limiting reactant.

32

• Part of the SO2 that is introduced into the
  atmosphere by combustion of sulfur containing
  compounds ends up being converted to sulfuric
  acid. The net reaction, 2SO2 O2 2H2O ?
  2H2SO4
• How much sulfuric acid can be formed from 5.0 mol
  SO2, 2.0 mol oxygen, and an unlimited quantity of
  water?

33

• 1. Determine the limiting reactant.
• 2. Calculate the unknown based on the limiting
  reactant.

34

• Consider the double replacement reaction between
  sodium phosphate and barium nitrate. Suppose a
  solution containing 3.50 grams of sodium
  phosphate is mixed with a solution containing
  6.40 grams of barium nitrate. How many grams of
  barium phosphate can be formed?

35

• 1. Write a balanced equation.
• 2. Determine which solution is the limiting
  reactant.
• 3. Calculate the unknown using the limiting
  reactant.

36
Theoretical Yield

• The quantity of product that is calculated to
  form when all of the limiting reactant reacts.
• Actual Yield amount of product actually
  obtained in a reaction
• Percent Yield relates the actual yield to the
  theoretical yield.