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CHEMISTRY 104
CHAPTER 5: CHEMICAL REACTIONS
Homework problems: 17, 21, 23, 27, 31, 33, 35, 41, 49, 51, 53, 57, 61, 63, 67, 73, 75,
81, 83, 85, 89, 93
Outline
I.
II.
Terms
A. Reactions
1. reactant(s)  product(s)
B. Molecular mass revisited
1. also called molecular weight, formula mass, formula weight
2. same concept as atomic mass, but for molecules instead of atoms
C. Mole
1. Avagadro’s number = 6.02214199… x 1023
2. just a number, like a dozen or a gross or a quarted
3. a very large number, but exactly what you need to go from amu
to grams
Chemical Equations
A. Reactants and Products
B. Balanced by atoms AND charge AND mass
1. Coefficients
2. implied “1” if nothing written
a. like you to write it anyway for now
3. lowest whole number ratio
C. How to balance
1. method on p137 or…
2. another way
a. find biggest, ugliest molecule
b. put a “1” down as its coefficient
c. work your way back and forth from reactant to
product to get ratio with ugliest molecule
d. when all done, multiply through (if necessary) to
get whole number ratio
3. Cannot change formulas in eqn to balance it!
D. Symbols of state (s, l, g, aq)
E. Stoichiometry
1. balanced eqn coefficients = moles (or molecules), NOT units mass (g)
2. grams A  moles of A  moles B  grams B
a. THIS is how you compare mass
b. This is stoichiometry
3. limiting reagent
a. what you run out of first
4. percent yield
a. actual yield
b. theoretical yield
c. % yield = actual yield/theoretical yield
III.
Reactions
A. Aqueous solutions (stuff is dissolved in water)
1. what happens when ionic stuff dissolved in water
2. polyatomic ions do NOT separate into individual atoms
3. Table of solubilities
a. how to tell if a reaction occurs using table
4. Equations
a. molecular equation
b. total ionic equation
c. net ionic equation
d. spectator ions
B. Redox reactions
1. what is oxidation and reduction
a. loss and gain of electrons
b. oxidation number (O.N.) rules
i. any element by itself, O.N. = 0
ii. any elemental (simple) ion, O.N. = charge
on ion
iii. for H in a molecule, O.N. = +1
iv. for O in a molecule, O.N. = -2
v. sum of O.N. in any molecule or ion = charge
2. Mnemonics
a. OIL RIG
b. LEO says GER
3. redox reaction examples
a. combustion
b. breathing/respiration
c. rust
d. bleach
e. battery
C. Heat of reaction
1. exothermic/exergonic
2. endothermic/endergonic
Chapter Objectives
Knowledge
Memorize the rules for determining oxidation number (?)
Recall number of items in a mole to 3 sig figs (6.02 x 1023)
Know the terms exothermic, endothermic, reducing and oxidizing agents, oxidation
number, percent and theoretical yields, limiting reagent
Comprehension
Be able to identify a reaction as redox (change in # of electrons) or not
Identify oxidizing and reducing agents in a redox reaction
Identify spectator ions in a Full Ionic Eqn
Identify a rxn as exo- or endothermic if told heat of reaction is positive or negative
Identify a limiting reagent
Application
Use mw to convert back and forth between mass and moles
Balance a chemical eqn
Determine Oxidation numbers using rules (?)
Write Net Ionic Eqns from Total Ionic Eqns
Analysis
Convert freely between Grams of X  moles of X  moles of Y  grams of Y
Calculate theoretical and percent yield