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CHEMISTRY 104
CHAPTER 6: CHEMICAL REACTIONS
Homework problems:
Outline
I. Terms
A. Reactions
1. reactant(s)  product(s)
H2SO4 (aq) + 2 NaOH (aq) → Na2SO4
+
2 H2O (l)
2. coefficients
3. reaction conditions
4. Symbols of state (s, l, g, aq)
5. exothermic and endothermic
a. exothermic: heat out (product) like in combustion
b. endothermic: heat in (reactant) like melting an ice cube (except
that is a physical change, and not a chemical one)
6. balanced equations
B. Balanced by atoms AND charge AND mass
1. Coefficients
2. implied “1” if nothing written
a. I would like you to write “1” anyway for now
3. lowest whole number ratio
C. How to balance
1. method on p145 or…
2. another way
a. make molecular formulas 1st!
b. find biggest, ugliest molecule
c. put a “1” down as its coefficient
d. work your way back and forth from reactant to product to get ratio
e. when all done, multiply through (if necessary) to get whole number ratio
f. Cannot change formulas in eqn to balance it!
g. You learned how to make ionic molecules earlier, don’t unlearn now!
II. Avagadro’s Number
A. Mole
1. Avagadro’s number = 6.02214199… x 1023 (only need to remember to 3 sf)
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
4. a measurement, not a count! (not infinite sig figs)
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
3. mw in g/mole same number value as amu/molecule (or amu/atom)
C. Converting grams → moles using mw= g/mole
1. examples: 62.4 g C= ? moles of C
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62.4 g water = ? moles of water
2. convert moles → atoms or molecules
examples: 62.4 g C= ? atoms of C
62.4 g water = ? molecules of water
III. Stoichiometry
A. balanced eqn coefficients = moles (or molecules), NOT units mass (g)
1. but measurements made in mass, so need to convert to compare
2. grams A  moles of A  moles B  grams B
a. THIS is how you compare mass (This is stoichiometry)
Examples: given 4 Fe
+
3 O2 
2 Fe2O3
How many g oxygen to rust 2250 g iron
IV. Limiting Reagent and Yields
A. Limiting Reagent: what you run out of first
Example: 400 g of iron, 300 g of iron, which is limiting?
B. Percent yield
1. Actual yield: what you get from experiment
2. Theoretical yield: what you should get if everything is perfect
3. % yield = (actual yield/theoretical yield)
a. should never be more than 100% or guaranteed something is wrong
V. Three reactions we will examine
A. Precipitation
1. A denser phase is created out of a lighter phase, like (s) or (l) from gas, or (s) from (aq)
2. Usually used when insoluble (s) phase forms in (aq) solution
B. Acid/Base
1. Acid + Base → Salt + Water (neutralization rxn)
C. Redox
1. One reactant is reduced, while another is oxidized – hence, redox
2. Classic redox rxn is combustion, where oxidized reactant gains oxygen and O2 is
reduced
3. Broader definition: oxidation is loss electrons, reduction is gain
4. Other examples: corrosion and purification of metals, respiration, bleaching
VI. Precipitation
A. Aqueous solutions (stuff is dissolved in water)
1. what happens when ionic stuff dissolved in water
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2. polyatomic ions do NOT separate into individual atoms
3. Table of solubilities (p164)
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
VII. Acid/Base Rxns
A. will talk about briefly here, but won’t study until Chem 105
VIII. Redox Rxns
A. 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
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Chapter Objectives
Knowledge
Memorize the rules for determining oxidation number (written in this outline)
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 # oxidation number) 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
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