Reactions
B. Seven Diatomic Elements
• (Super Seven) never appear alone in
nature. They are chemically combined in
compounds or with themselves. These
include hydrogen, nitrogen, oxygen,
fluorine, chlorine, bromine, and iodine.
• H2, N2, O2, F2, Cl2, Br2, I2
IV. Types of Chemical Reactions
A. Combination or Synthesis
1. A reaction in which two or more
substance combine to form a single
product
2. Examples:
2. Examples:
•
•
•
•
•
2H2 + O2  2 H2O
4Al + 3O2  2Al2O3
Ca + Cl2  CaCl2
2KCl + 3O2  2KClO3
Notice that in each example, a
compound is formed from elements
or smaller compounds. This may be
represented by the following general
equation: A + B  AB
B. Decomposition Reaction
1. A reaction in which a compound is broken
down into simpler substances such as
elements or smaller compounds
2. Examples
2. Examples
• 2HgO
• 2H2O
∆
2Hg + O2
𝑒𝑙𝑒𝑐𝑡𝑟𝑐𝑖𝑡𝑦
𝐶𝑎𝑡𝑎𝑙𝑦𝑠𝑡
2H2 + O2
• 2 KClO3
2KCl + 3O2
• Decomposition reactions are generally
the opposite of composition reactions.
Such a reaction may be represented by
the following general equation:
AB  A + B
C. Single Replacement Reaction
1. A reaction in which one element reacts
with a compound to form a different
element and another compound
2. Examples
2. Examples
•
•
•
•
Cu + 2AgNO3  Ag + Cu(NO3)2
Zn + Cu(NO3)2  Cu + Zn(NO3)2
Mg + 2HCl  H2 + ZnCl2
These reactions occur according to the activity
series of metals. Elements on the top of the
list may replace elements below them in a
chemical reaction. For the Halogens, elements
may replace those below them in the group.
• The general equation for a single replacement
reactions looks like: A + BC  B + AC
D. Double Replacement Reactions
1. A reaction in which the metals (or cations)
present in two compounds changes places
to form two new compounds.
2. Examples
2. Examples
• AgNO3 + NaCl  AgCl + NaNO3
• NaOH + HCl  NaCl + H2O
• Ba(NO3)2 + Na2SO4  BaSO4 +
2NaNO3
• The general equation for a double
replacement reactions is:
AB + CD  AD + CB
• These reactions often use the solubility
rules to predict precipitate formation.
E. Combustion Reaction
1. A reaction in which oxygen reacts
with another substance usually
producing heat and light. (We will be
dealing primarily with the combustion
of hydrocarbon fuels)
2. There are two kinds of combustions:
complete combustion and
incomplete combustion
3. Examples
• CxHy + O2  CO2 + H2O
• CxHy + O2  CO + C + H2O
4. Elemental carbon or soot, among
other things may be formed during
incomplete combustion.
F. Oxidation – Reduction Reactions
1. A reaction in which the oxidation number of an
element changes.
2. Think of a number line. If the oxidation number
moves to the right on the number line (becomes
less negative or more positive) the element is
oxidized. If the oxidation number moves to the
left on the number line (becomes more negative
or less positive) the element is reduced.
3. To calculate the oxidation of the element, use the
charge of the element or polyatomic ion to
determine the charge of the metal in each
substance. Elements in their natural state have
an oxidation number of zero.
4. Examples
• Ag + NaCl  AgCl + Na
• Al + Cu(NO3)2  Cu + Al(NO3)3
5. For this course, we will concentrate on
oxidation-reduction reactions that are
also single replacement reactions, but
others do exist.
G. What type of chemical reaction is
represented by the following
equations?
• SR • Ca + BaO  Ba + CaO
• CB • 2C3H6 + 9O2 6CO2 + 6H2O
• S
• Ca + O2  CaO
• DR • Na3PO4 + BaCl2  Ba3(PO4)2 + NaCl
• D
• MgCl2  Mg + Cl2
H. Nuclear Reactions
1. A reaction in which nucleotides (particles)
react during nuclear fusion or fission.
2. Fusion – is the combination of two smaller
nucleotides for form a larger, more
massive particle. This is what happens in
our sun.
3. Fission – is the splitting of a large,
unstable nucleotide into smaller particles.
This occurs in nuclear reactors.
4.The particles involved include the following
• Alpha particles, a, look like helium ions: 𝟒𝟐𝑯𝒆𝟐+
• Beta particles, b, look like electrons: −𝟏𝟎𝒆
• Positrons look like positive beta particles: +𝟏𝟎𝒆
• Neutrons are just neutrons: 𝟏𝟎𝒏
• Protons are often written as hydrogen ions: 𝟏𝟏𝑯+
• Gamma Rays – really a form of radiation that
accompanies many nuclear reactions: 00𝛾 or just g
5. To balance a nuclear reaction, make sure the
total mass numbers on each side of the
reaction are equal and the total atomic
numbers on each side are equal.
6. Examples
6
4
2
• 3Li + 1H → 2He + 𝟒𝟐𝐇𝐞
6+2=4+x
x=4
3+1=2+y
y=2
•
14
6𝐶
•
238
92𝑈
•
234
+
→
1
1𝐻
234
𝑇ℎ →
→
1
0𝑛
+
𝟏𝟒
_____
𝟕𝐍
𝑇ℎ + _____
234
𝑃𝑎 + _____
7. Radiation
• Alpha radiation is the least penetrating. It
can be stopped by a piece of paper. This
is because of the size of the particles.
• Beta radiation is moderately penetrating.
Aluminum foil is thick enough to stop beta
radiation.
• Gamma radiation is the most penetrating
because it is a form of electromagnetic
radiation. Layers of concrete and lead are
needed to stop gamma radiation.