CHAPTER 10: CHEMICAL
REACTIONS
I.
Reactions & Equations
A. Chemical reaction (rxn): process by which
atoms of one or more substances are
rearranged to form different substances
B. Evidence of Reactions (video)
1.
2.
3.
4.
5.
6.
7.
Energy is taken in or given off
Gases are given off (bubbles)
Permanent color changes
Odor
Precipitate (solid) is formed from solutions
Smoke and/or soot
Surface changes (ex: rust)
C. Representing Chemical Reactions
1.
Chemical equation: condensed statement of facts
about a chemical reaction; shows number & type of
atoms present before & after reaction
a. Obeys law of conservation of mass: same # of atoms
before & after
2.
General format:
reactant 1 + reactant 2 → product 1 + product 2
a. Reactants: substances present before the reaction
b. Products: substances present after the reaction
c. Symbols:
3. Writing an equation:
Observation: hydrogen burns with oxygen to form water
Word equation: hydrogen gas + oxygen gas → water
Skeleton equation: H2(g) + O2(g) → H2O(l)
Balanced equation: 2H2(g) + O2(g) → 2H2O(l)
a.
b.
c.
d.
i.
Phase symbols are often dropped & substances are
assumed to be in their normal state
2H2 + O2 → 2H2O
ii.
Example:
e.
i.
ii.
iii.
iv.
Observation: carbon and sulfur react to form carbon disulfide
Word equation: solid carbon + solid sulfur → liquid carbon
disulfide
Skeleton equation: C(s) + S(s) → CS2(l)
Balanced equation: C(s) + 2S(s) → CS2(l)
D. Balancing Chemical Equations
1. Terminology:
a. Coefficient: number placed to the left of the
reactant or product; indicates the number of
particles involved in the reaction
i.
Example: 2H2O, 3C6H12O6, 5NaCl
b. Subscript: number to the lower right of the
element symbol; indicates the number of atoms
of a particular element
i.
Example: CO2, H2SO4, Na3PO4
2. Steps in balancing an equation:
a.
Write a skeleton equation using the correct formulas for
all reactants & products
**do NOT mess with subscripts after this point**
Count the number of atoms of each element on each
side of the equation
Balance the equation using coefficients
b.
c.
i.
ii.
iii.
d.
Atoms in = atoms out
Start with the first element on the left & balance each
element moving right -- save hydrogen & oxygen for last
Coefficients must be in the lowest possible ratio (so if it’s
2:4, reduce to 1:2)
Check your work!
3. Examples:
a. Write the balanced chemical equation for the
reaction in which sodium hydroxide and calcium
bromide react to produce solid calcium
hydroxide. The reaction occurs in water.
b. Propane (C3H8) reacts with oxygen to form carbon
dioxide and water. Write a balanced equation for
this reaction.
Homework:
 p. 279: 1-3
 p. 282: 4-6 (show all steps!)
 p. 283: 7-13 (13 – show all steps!)
II. Classifying Chemical Reactions
A. Five major types:
1. Synthesis: two or more substances combine to
form one new substance
a. Form: A + B → AB
b. Example: 2H2 + O2 → 2H2O
c. May also involve two compounds combining to
form one compound, or one compound and one
element combining to form a compound
2. Combustion (oxidation reactions): oxygen
combining with a substance to produce heat
and usually light; typically burning
a. Form: substance + oxygen → product(s) + light +
heat
b. Example: CH4 + 2O2 → CO2 + 2H2O
3. Decomposition: one substance breaks down
into simpler substances
a. Form: AB → A + B
b. Example: 2HgO → 2Hg + O2
c. Usually require an energy source to occur
4. Single replacement: one element and one
compound combine -- the single element
replaces (switches places with) one of the
elements in the compound.
a. Form: A + BX → AX + B
b. Example: Zn + 2HCl → ZnCl2 + H2
5. Double replacement: positive and negative ions
of the two compounds are interchanged
a. Form: AX + BY → AY + BX
b. Example: NaCl + AgNO3 → NaNO3 + AgCl
B. Reactions may be more than one type
1. Example: C + O2 → CO2 -- combustion &
synthesis
2. Example: CH4 + 2O2 → CO2 + 2H2O -combustion & single replacement
Homework
 Copy Table 10-3
 p. 291: 24-30
 Worksheet (both sides)
III. Reactions in Aqueous Solutions
A. Aqueous solutions: solutions in which the
solutes are dissolved in water
1. Three types:
a. Molecular compounds that exist as molecules
when dissolved in water (ex: table sugar in grain
alcohol)
b. Molecular compounds that form ions in water (ex:
HCl dissociates into H+ & Cl- ions)
c. Ionic compounds that form ions in water (ex:
NaOH dissociates into Na+ & OH- ions; NaCl
dissociates into Na+ & Cl- ions)
B. 3 possible results when two aqueous solutions
that produce ions are combined in double
replacement reactions
May produce a precipitate: a solid produced in a
chemical reaction
1.
a.
2.
Ex: 2NaOH(aq) + CuCl2 (aq) → 2NaCl(aq) + Cu(OH)2(s)
May produce water
a. This will always contain an acid, which produces H+
ions, and a base producing OH- ions
b. No evidence of a chemical rxn is observable
c. Ex: HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)
3. May produce a gas
a. Evident due to bubbles of gas leaving the
solution
b. Gases commonly produced: O2, CO2, H2S, HCN
c. Ex: 2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)
Homework
 All of the following problems ask for the chemical, ionic,
and net ionic equations – we are ONLY doing chemical
equations
 p. 294: #33-37 (#34 has no reaction, so for the
products, put “NR”)
 p. 296: #38-42
 Worksheet
C. Simultaneous Chemical Reactions
1. Sometimes when 2 solutions are mixed, 2 or
more reactions happen at the same time
2. Ex: sodium bicarbonate powder dissolves in
hydrochloric acid to produce carbonic acid and
aqueous sodium chloride; as the carbonic acid
is formed, it immediately breaks down into
water and carbon dioxide.
a. Equations:
i.
ii.
NaHCO3 (aq) + HCl (aq) → H2CO3 (aq) + NaCl (aq)
H2CO3 (aq) → H2O (l) + CO2 (g)
b. These two reactions can be combined – put all of
the reactants on one side, and all of the products
on the other
i.
NaHCO3 (aq) + HCl (aq) + H2CO3 (aq) → H2CO3 (aq)
+ NaCl (aq) + H2O (l) + CO2 (g)
c. Then cancel out anything that appears on both
sides
i.
NaHCO3 (aq) + HCl (aq) → NaCl (aq) + H2O (l) + CO2
(g)
Homework
 p. 299 #43-46 (chemical equations only)
 p. 299 #47, 49, 51
Review
 p. 303 Vocab (17 words)
 p. 304 Concept Map
 p. 304 Mastering Concepts #53-66, skip 65
 p. 304-6 Mastering Problems #71-94
(do not need to write ionic or net ionic equations)
 p. 306 Mixed Review #95-100