1. Stoichiometry: Calculations with Chemical Formulas & Equations
Chapter 3
Stoichiometry: Calculations with Chemical Formulas & Equations

2. Stoichiometry & Chemical Eq’ns
Stoich: the study of the rearrangement of atoms in molecules during chemical rxns
Chem eq’n: the written expression of a chemical process
Subscripts: denote the number of each atom in a chemical formula; used to balance charge; are not changed when balancing rxns
Coefficients: denote the number of molecules in a rxn; may be changed to balance a rxn; demonstrate LOCOM

3. Patterns of Reactivity
Alkali & alkaline earth metals react with water to produce a metal hydroxide and hydrogen gas
Metal oxides react with water to produce metal hydroxides
Nonmetal oxides react with water to produce oxyacids
Hydrocarbons react with oxygen gas to produce carbon dioxide & water

4. Patterns of Reactivity (cont)
5. Metals and oxygen produce metal oxides
6. Nonmetals and oxygen produce nonmetal oxides
7. Acids and bases produce water and a salt
8. Metals and nonmetals produce salt
9. Metals and acids react to produce hydrogen gas and a salt

5. Patterns of Reactivity (cont)
10. Metal oxides and nonmetal oxides produce salts
11. Aqueous compounds may react to form precipitates
12. Ammonium ions plus a metal hydroxide produce water, ammonia gas, and a salt
13. Metal hydrides and water produce metal hydroxides and hydrogen gas

6. Patterns of Reactivity (cont)
14. Metal hydrides and oxygen produce metal oxides and water
15. Peroxides decompose into oxygen gas
16. Metal nitrides and water produce ammonia and a metal hydroxide
17. Hydrogen carbonates and hydrogen sulfites react with acids to produce carbon dioxide (or sulfur dioxide), water and a salt

7. Patterns of Reactivity (cont)
18. Superoxides react with water to produce oxygen gas, hydrogen peroxide, and aqueous alkali and hydroxide ions
19. Metal carbides and water produce acetylene (C2H2 - explosive) and a metal hydroxide
20. Ammonia and hypochlorite ions react to produce water, salt, and hydrazine gas (N2H4- deadly poisonous)

8. Atomic & Molecular Weights
1 amu = x10-24g
1 g = x1023 amu
Average atomic mass: the weighted average of all naturally occurring isotopes
Formula weight: sum of the average atomic masses of all elements in the compound; also known as molecular weight for molecular substances

9. Percent Composition
The percent by mass of each element compared to the total mass of the entire compound

10. Mole & Molar Mass
A unit of quantity; represents the amount of a substance
Avogadro’s number = 6.02x1023
Molar mass: the mass of 1 mol of any substance is equal to its atomic mass in grams
1 mol 12C = g

11. Mole Conversions
We can interconvert mass, moles and amount
Mole Map:

12. Mass Spectrometer
An instrument used to determine atomic and molecular masses
Gaseous samples of an element are ionized, then accelerated through a magnetic field
Deflection of ions with identical charge depends upon mass
More mass = less deflection
Results in a unique signature of isotopic abundance

13. Determining Empirical Formulas
Using mass percentage or mass itself, convert into moles by dividing by atomic mass
Determine molar ratio by dividing by the lowest number of moles
Multiply by whole numbers until ratio is most nearly equal to whole numbers
Write formula

14. Determining Molecular Formulas
Determine formula mass of empirical formula
Determine mass ratio for empirical and molecular formula
Multiply empirical formula by the whole number determined from mass ratio

15. Combustion Analysis
Many samples are determined through combustion analysis
Determine moles of C and H first
Subtract from initial mass to determine moles of O
Determine molar ratios and write formula

16. Balanced Equations & Quantitative Information
Coefficients denote molar ratios of compounds
We can solve molar calculations using these ratios in proportion with a balanced chemical reaction

17. Limiting Reactant
The reactant in a chemical process that is entirely consumed; determines the amount of product made in the reaction
Any reactant could be the limiting reactant - it depends on a particular set of conditions

18. Theoretical, Actual, & % Yield
The amount of product one expects based upon the molar ratios and amounts of reactants involved in the chemical process
Actual Yield – the amount of product recovered in the experiment
Percent Yield = actual/theoretical x 100