Name: _____________________________________________
Chemical Reactions
I. Chemical reactions are changes which produce _______ substances.
a. Bonds between atoms are broken (covalent bonds, metallic bonds, and/or ionic bonds), atoms
scramble around, and the atoms then re-connect to form different substances. Saying that a
“chemical reaction” has occurred, is identical to saying that a “chemical change” has occurred.
b. Sometimes the new substances produced are in a different state (and sometimes not).
c. A change of state (by itself) does not produce a new substance.
i. A change of state is just melting/freezing, boiling/evaporation/condensation, or
sublimation/deposition. The substance itself doesn’t change during a change of state.
d. Atoms are ____________ created or destroyed during chemical reactions.
i. Since atoms have mass: mass is ______ created or destroyed during chemical reactions.
ii. Since mass is not gained or lost during a chemical reaction, we say that mas is
________________________.
iii. The name of this fact is called the “law of ________________________ of _________”.
II. When asked to write a “_______________________ ______________________”, we use formulas and
symbols (to represent the compounds and elements) which take part in the chemical reaction.
a. For example, instead of saying, “hydrogen peroxide” changes into “water” and “oxygen”, we
would use the formulas, H2O2 and H2O, and the symbol O2.
b. An arrow is placed within a chemical equation, to separate the substances present before the
reaction begins, from those present after the reaction occurs. The arrow means “yields” (or
“produces”).
i. For example, H2O2  H2O + O2 would be the first step toward writing the final
chemical equation for this reaction; and it would be read aloud as “H2O2 ____________
water _______ oxygen,” or, “H2O2 ________________ water _____ oxygen”
c. The substances to the left of the arrow are referred to as the ___________________ (because
they are allowed to “react” together, while the substances to the right of the arrow are referred
to as the _____________________ (because they are what are “produced” during the reaction).
d. The example, H2O2  H2O + O2 is not the final complete chemical equation; in fact, it is not
yet even yet a complete ______________________ equation.
e. Skeleton equations show the reactants to the right, and the products to the left, of the arrow;
and, additional information that is known about the substances should also be included within
the skeleton equation. The additional information will be shown by using accepted symbols.
i. Designates a substance as being in the solid state: ____________________. Appears
after the substance.
ii. Designates a substance as being in the liquid state: ___________________. Appears
after the substance.
iii. Designates a substance as being in the gaseous state: _________________. Appears
after the substance.
iv. Designates the substance as being dissolved (or remains dissolved) in an aqueous
solution (a solution containing water): __________________. Appears after the
substance.
v. A double-ended arrow replaces  when a reaction is _____________________
1. This occurs when the new substances just formed (the products), react together
and regenerate the original substances (the original reactants)

vi. An arrow with a triangle over it (or an arrow with the word heat over it) indicates that
heat is supplied to the reaction.
vii. An arrow with a chemical (a formula or a symbol) written above or below it indicates
that the chemical is being used to speed up the chemical reaction.
Formula or symbol
1. The general term for a chemical which speeds up a reaction is:
_________________.
2. A catalyst does NOT “enter into” the reaction; it just quickens it.
3. A catalyst is present at the start of, during, and at the end of a reaction; but, since
it doesn’t change into a different substance, it is NOT a reactant or a product.
f. What is not written in a skeleton equation?
1. The relative ________________ of each substance in the reaction.
g. How do you determine the products of a chemical reaction?
i. Only by actually _______________________ the reaction!
ii. This is because several chemicals may react together, under slightly different conditions,
to produce different products.
h. You should never see the same substance both to the left side and to the right side of the arrow.
i. During this chapter, we assume the reaction is _________________. This means, each
substance that is present before the reaction begins will be completely changed into
something different; unless the chemical reaction is said to be “___________________”.
In that case, the reaction never “goes to completion”; instead the reactants react to make
the products, and simultaneously the products react to make the reactants…. Which react
to make the products….. which simultaneously react to make the reactants….. .
III. Balancing Chemical equations.
a. For each skeleton equation to become a complete (final form) chemical equation,
____________________ must be inserted into the skeleton equation.
i. Coefficients are whole numbers which indicate the relative _________________ of each
substance.
ii. A chemical equation is said to be “____________________” when, the number of atoms
of each element found on the reactant side of the equation is equal to the number of
atoms of that same element on the product side of the equation.
iii. In a balanced equation, each side of the equation will have the same numbers of
_____________of each element.
iv. To balance an equation, a coefficient is placed ________________ each substance in the
equation. The coefficient is a “multiplier”. It doubles, triples, quadruples (etc.) the
amount of the substance it is placed in front of.
v. The coefficients used for an equation should be the _____________________ whole
numbers possible to achieve balancing of the atoms.
b. Strategies or tips for balancing chemical equations.
i. Balance __________ element at a time; don’t try to balance the whole equation at once.
ii. First pick an element that appears in only _______ reactant and ________ product.
iii. Determine the LCM for the element you have picked. Ex (below) – let’s pick fluorine.
1. The subscripts are 2 and 3; the least common multiple of 2 and 3 is __________.
2.
Place a coefficient of ______ on the left and ______ on the right, so as to now
have 6 atoms of F both on the left and on the right.
Example:
_____Al
+ ______F2  _____AlF3
______ F2 
_____Al
+_
Think momentarily only about the LCM of “F” .
_____F3
3 F2  __2_ AlF3
(LCM of 2, 3 = 6)
(Remember, coefficients are ___________)
iv. After balancing one element, pick a second element to work with that appears in the
___________ compound as the already-balanced element. Again, determine the LCM.
Think momentarily only about the LCM of “Al”, in
___2__Al
+_
__ Al  __2 AlF3
3 F2  __2_ AlF3
You need at the moment the LCM of 1, 2 which is 2
is correct because 2 Al + 6 F  2 Al + 6 F
v. Start an atom inventory. The atom inventory for the above example is this:
2Al 6F
Only when the atom inventory is equal on both sides, is the balancing correctly done.
2Al 6F
vi. Balance these two atoms last: __________________ and __________________.
1. The reason is, many times H and O occur in 2 substances to the left of the arrow
and/or 2 substances to the right of the arrow.
2. When this occurs, you must ______ as well as multiply to solve the problem.
The example shown below will illustrate this point.
Notice the atom inventory:
_____ CH4 + _____ O2  _____ CO2 + _____H2O
Ex:
Balance the “C” first:
1C 4H 2 Ox
__1__ CH4 + _____ O2  __1__ CO2 + _____H2O
1C 2 Ox 2H 1 Ox
1C 2H
3 Ox
Balance the “H” second:
LCM of 4, 2 = 4
__1__ CH4 + _____ O2  __1__ CO2 + __2__H2O
1C 4H 2 Ox
1C 2 Ox 4H 2 Ox
1C
4H 4 Ox
Notice, to balance the “O”, you must now add the number of oxygen atoms from
two compounds (CO2, H2O): 1 CO2 has 2 oxygen atoms; 2 H2O also has
2 oxygen atoms. 2 + 2 = 4 oxygen atoms are on the right side.
LCM 2, 4 = 4
__1__ CH4 + __2__ O2  __1__ CO2 + __2__H2O
Aim for 4 oxys on
the left
This equation is correctly balanced, as shown by the atom inventory.
1C 4H 4 Ox
1C 4H 4 Ox
vii. If you are having difficulty with a combustion problem (or any problem), double a
coefficient and re-work the problem based on the assumption that the new double
coefficient is correct. This corrects problems with needing a “half” coefficient, which
1C 4H 2O
1C 4H 4O
might occur during combustion reactions in which there are an even number of carbon
atoms.
1. Ex:
2 ½ can’t be used as a coefficient; but, 5 can be used as a coefficient.
viii. As long as you have a ____________________________ ___________, both to the left
and to the right of the arrow, work with it as a whole unit (don’t work with it as
individual atoms).
Ex:
in Al(NO3)3, there are 3 (NO3)
ix. Re-write H2O as HOH whenever (OH) is present on the opposite side of the arrow from
H2O.
IV. The Five General Types of chemical reactions.
a. When you are shown a series of chemical equations, by distinguishing both
____________________ and _____________________, you will notice that there are 5
different types of common chemical reactions.
b. It is easiest to identify the 5 types of chemical reactions (or equations) by ignoring the
__________________________ -- The coefficients identify the relative amount of each
substance; but, they do not identify the type of chemical reaction!
c.
Once you know what to look for, you can learn to classify the reactions (or equations).
i. Unfortunately however, NOT every chemical reaction can be “classified” (placed into)
only one of the five general types!
ii. Some chemical reactions will fit within more than one of the 5 types. For this reason,
the examples that you will be given are hand-chosen for beginning chemistry students.
Below, when you see that I have written, “don’t worry about….,” it means that the
information is given as enrichment only, not required learning.
V. Synthesis reaction: A reaction in which _______________________ ___________________ to make
a compound. A + B  AB
a. Be careful to remember the 7 diatomic elements: N2, O2, F2, Cl2, Br2, I2, H2
Ex:
Al + F2  AlF3
b. [Do not worry about “photosynthesis”; but, photosynthesis is a synthesis reaction in which
small compounds combine to form a larger compound:
CO2 + H2O  C6H12O6 + O2
VI. Decomposition reaction: A reaction in which a single compound ________________ ____________
into its “constituent” elements. AB  A + B
a. In other words, “a single reactant is the identifying characteristic of a decomposition reaction,”
and, during “the decomposition of a simple binary compound”, the products are “predictable”,
as they are the elements found in the compound.
b. The starting compound might be either a _________________compound or an
_________________ compound.
c. Do not worry about “respiration”; but, during respiration (which begins with an intake of
oxygen) a decomposition reaction occurs, during which blood sugar (glucose, C6H12O6) is
broken down into carbon dioxide and water vapor:
C6H12O6 + O2  CO2 + H2O
VII.
Combustion reaction: A reaction in which there are 2 reactants. One reactant is usually a
hydrocarbon (a substance containing both ________________ and _________________); the
second reactant must be _____________. Remember, the symbol for oxygen is _______.
a. We will assume that the combustion is complete; therefore, there will only ever be 2 specific
products: __________ and ____________, both present in the _______________ state.
b. When complete combustion occurs, all of the carbon found within the reactant will be totally
converted into the product, carbon dioxide (CO2).
Ex:
__1__ CH4 + __2__ O2  __1__ CO2 + __2__H2O
Notice how it is easier to classify the example after removing the coefficients: CH4 + O2  CO2 + H2O
VIII.
Single-Replacement reaction: A reaction in which the reactants are 1 element + 1 ionic
compound; and the products are 1 different ______________ + 1 different ionic _______________.
a. In other words, “one element reacts with a compound to form a new compound and a different
element”. A + XY
Na + KCl


X + AY
K
+
NaCl
or
or
A + XY
F2
+
NaCl


Y
+ XA
Cl2
+ NaF
IX. Double-Replacement reaction: A reaction in which the reactants are 2 ______________ compounds,
and the products are both compounds; however, at least one of the following conditions must occur.
a. At least 1 product is a binary molecular compound (this means that the compound has 2
different non-metal elements). Ex: H2O
b. A least 1 product is in the gaseous state. Ex: CO2
c. Or, at least 1 product is in the solid state (or said to “precipitate” or be a “precipitate”).
Ex: PbCl2 (s)
X. Learning how to “predict the products”:
a. You will be asked to predict the products for (and then balance) a given combustion reaction.
i. Don’t worry about it! The products of any combustion reaction are _______ and
_______.
ii. Balance the __________________ atoms first. If there are an even number of carbon
atoms, ______________ the coefficients that you think you should use!
iii. Balance the ___________________ atoms second. Save the _______________ atoms
till last because you will have to ___________ together the oxygen atoms from CO2 and
H2O.
iv. Practice: Predict the products and balance:
C3H8
+
O2 
b. You will be asked to predict the products for (and then balance) a given single-replacement
equation, which is given in the form of: ionic compound + metallic element  ?
(Remember:
XY
+
A

X
+
AY
change places
ionic compound + metallic element  single atom + new ionic compound
i. Step 1: Take the cation out of the ionic compound, and place the cation (as a single atom) to the
right of the arrow. Position the “+” sign after it.
ii. Step 2: Take the symbol of the metallic element and position it after the “+” sign. The metallic
element will become the “new cation” for the new ionic compound.
iii. Step 3: Take the anion out of the ionic compound, and place the anion to the right of the new
cation.
iv. Step 4: Make the new ionic compound neutral (….Do a swap/drop/and simplify).
v. Practice – Predict the products and balance, CaSO4 + Na 
c. You will be asked to predict the products for (and then balance) a given single-replacement
equation which is given in the form of: ionic compound + halogen  ?
(Remember:
XY
+
A2

Y2
+
XA
change places
ionic compound
+
diatomic halogen  new diatomic halogen + new ionic compound
i. Step 1: Take the anion out of the ionic compound, and place the anion (as a diatomic atom) to
the right of the arrow. Position the “+” sign after it.
ii. Step 2: Take the cation from the ionic compound, and position it after the “+” sign.
iii. Step 3: The original diatomic halogen will now become the “new anion” for the new ionic
compound. The halogen will not necessarily keep it’s original “2” subscript.
iv. Step 4: Make the new ionic compound neutral (….Do a swap/drop/and simplify).
v. Practice – Predict the products and balance, NaI + Cl2 
d. You will be asked to predict the products for (and then balance) two given double-replacement
equations.
Ionic compound + ionic compound  ?
i. Step 1: Exchange the two cations.
ii. Step 2: Make each of the new ionic compounds neutral (….Do a swap/drop/and
simplify).
iii. Practice – Predict the products and balance, Ba(C2H3O2)2 + NaCl  ?