Stoichiometry Calculations with Chemical Formulas and Equations

1
StoichiometryCalculations with Chemical
Formulas and Equations

• Chapter 3 BLB 11th

2
Stoichiometry

• Quantity relationships based on chemical
  equations
• 3 Main Concepts
• Chemical formula molar ratio of atoms
• Chemical equations molar ratio of compounds
• Law of Conservation of Mass
• mass of reactants mass of products

3
3.1 Chemical Equations

• Components
• reactants ? products
• Physical states (s, l, g, aq)
• Reaction conditions (heat, light, solvents, etc.)
• Coefficients determine molar ratios. The number
  of moles of each type of atom must be the same on
  each side.
• Balancing
• By inspection
• Use coefficients dont change chemical formulas

4

• Fe2S3(s) HCl(aq) ? FeCl3(s)
  H2S(g)
• KClO3(s) ? KCl(s) O2(g)
• HNO3(l) P4O10(s) ? (HPO3)3(l)
  N2O5(g)

5
3.2 Some Simple Patterns of Chemical Reactivity

• Combination and Decomposition
• combination A B ? C
• 4 Fe(s) 3 O2(g) ? 2 Fe2O3(s)
• decomposition C ? A B
• 2 NaN3(s) ? 2 Na(s) 3 N2(g)

6
3.2 Some Simple Patterns of Chemical Reactivity

• Combustion
• burning of a fuel in the presence of oxygen
• products of complete combustion are carbon
  dioxide and water
• exothermic (produces heat)

7
Molecular view of methane combustion
8
3.2 Some Simple Patterns of Chemical Reactivity

• Combustion
• C3H8(g) 5 O2(g) ? 3 CO2(g) 4 H2O(g)
• 2 CH3OH(g) 3 O2(g) ? 2 CO2(g) 4 H2O(g)
• Each C atom in fuel produces 1 mol CO2
• Each H atom in fuel produces ½ mol H2O

9
3.3 Formula Weights

• Formula and Molecular Weights (amu)
• formula weight general
• molecular weight molecules
• formula unit weight ionic compound
• - sum of the atomic masses of each atom in
  chemical formula

10
Composition

• composition by mass
• Mass of one type of atoms over mass of all atoms

11
(No Transcript)
12
3.4 The Mole

• Word association
• pair -
• dozen
• case
• ream

13
3.4 The Mole

• amu impractical for lab use (too small)
• Avogadros number 6.0221421 x 1023 mol-1
• The number of atoms in exactly 12 g of 12C
• 1 mole Avogadros number of anything
• molar mass mass in grams of one mole g/mol

14
Practice with Avogadros
15
3.4 The Mole

• Atoms compounds have different masses, thus the
  mass of 1 mole of atoms compounds are
  different.
• g ? mol divide by molar mass
• mol ? g multiply by molar mass
• Abbreviations mole mol
• molarity M

16
3.5 Empirical Formulas from Analyses

• Empirical formula smallest whole number ratio
  of atoms
• Molecular formula actual ratio of atoms in a
  compound multiple of the empirical formula must
  know molar mass of compound
• Use composition to find formula
• Problems

17
A once-used gasoline additive contains 49.5 C,
3.2 H, 22.0 O, and 25.2 Mn. Determine the
emipirical formula of this compounds.
18
Azulene, a hydrocarbon, contains 93.71 C. Its
molar mass is 128 g/mol. Determine the
emipirical and molecular formulas for azulene.
19
3.5 Empirical Formulas from Analyses

• Combustion analysis
• 1 mol C in fuel ? 1 mol CO2
• 2 mol H in fuel ? 1 mol H2O
• Problems

20
The combustion of propane, a hydrocarbon,
produces 2.641 g CO2 and 1.442 g H2O. Determine
the emipirical formula of propane.
21
3.6 Quantitative information from Balanced
Equations

• 3 Main Concepts
• Chemical formula molar ratio of atoms
• Chemical equations molar ratio of compounds
• Law of Conservation of Mass
• mass of reactants mass of products

22
Stoichiometry Problems

• Use these 4 steps as a guide (p. 100)
• Write balance chemical equation.
• Convert to moles.
• Apply molar ratio.
• Convert from moles to quantity desired (mass,
  volume, etc.)

23
How many grams of CaCl2 is produced from taking 2
antacid tablets, each containing 500. mg of
CaCO3?CaCO3(s) 2 HCl(aq) ? CO2(g) H2O(l)
CaCl2(s)
24
3.7 Limiting Reactant

• Limiting reactant reactant which is completely
  consumed and limits the amount of product that
  can be formed
• Theoretical yield calculated yield of a product
  based on limiting reactant
• Percent yield

25
72. Calculate the theoretical yield (in grams) of
NO when 2.25 g of NH3 react with 3.75 g of O2.
NH3(g) O2(g) ? NO(g) H2O(g)
26
Silver metal reacts with elemental sulfur
according to the reaction below. If 2.0 g each
of silver and sulfur react, what is the
theoretical yield (in grams) of silver(I)
sulfide? How many grams are left over? 16
Ag(s) S8(s) ? 8 Ag2S(s)
27
How many grams are left over? 16 Ag(s)
S8(s) ? 8 Ag2S(s)
28
78. When hydrogen sulfide gas is bubbled into a
solution of sodium hydroxide, the reaction forms
sodium sulfide and water. How many grams of
sodium sulfide are formed if 2.00 g of hydrogen
sulfide is bubbled into a solution containing
2.00 g of sodium hydroxide, assuming that the
sodium sulfide is made in 92.0 yield?
29
(No Transcript)
30
When 0.750 g iron(III) chloride hydrate is
heated, 0.300 g of steam is produced. What is
the value of x ? FeCl3x H2O(s) ? FeCl3(s)
x H2O(g)
?
31
(No Transcript)