Name: _____________________________________________________
UNIT
CHEMICAL REACTIONS
Parts of a Chemical Equation:
4 Fe + 3 O2
2 Fe2O3
Reading a Chemical Equation:
4 Fe(s) + 3 O2(g)
2 Fe2O3(s)
Four moles of solid iron reacts with three moles of gaseous oxygen to produce two moles of solid iron(III) oxide
(s) means solid
(l) means liquid
(g) means gas
(aq) means aqueous (which means mixed with water)
Reactants
Products
Always in
this order!
Chemical reaction: chemical change that forms new substances with new properties by rearranging atoms
New atoms are NOT formed in a chemical reaction. Atoms are NOT destroyed in a chemical reaction.
4 Fe + 3 O2
2 Fe2O3
In a chemical reaction the bonds of the reactants are broken and the bonds of new products are formed
2 H2O → 2 H2 + O2
BARF: When bonds are Broken energy is Absorbed; energy is Released when bonds are Formed
Four indications (clues) that a chemical reaction may have occurred:
1. color changes
2. gas is produced (bubbles)
3. precipitate formed
4. temperature changes (not phase changes)
The LAW of CONSERVATION of MASS
In a chemical reaction,
THE MASS OF THE PRODUCTS IS EQUAL TO THE MASS OF THE REACTANTS
No atoms are formed, No atoms are destroyed
The atoms have been rearranged!
The total mass of the system is always the same (conserved)!
The same number of the same types of atoms that were in the
reactants before the reaction started are present in the products
at the end of the reaction.
REACTANTS
PRODUCTS
THE MASS OF THE PRODUCTS IS EQUAL TO THE MASS OF THE REACTANTS
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ConservationofMass.m4
v
Balancing Chemical Equations
The Law of Conversation of Mass:
Mass of Reactants = Mass of Products
The same number of the same types of atoms
that were in the reactants before the reaction started
are present in the products when the reaction is over!
The products contain the same number of the same types of atoms that were in
the reactants!
The atoms have been rearranged!
This equation is balanced as it is
C + O2
Both sides of the reaction
have the same number of
the same types of atoms!
Reactants
C: 1
O: 2
→ CO2
=
Product
C: 1
O: 2
EXAMPLE:
This equation is NOT balanced
First, get the initial atom counts
Fe + S2 →
Reactants
Fe: 1
S: 2
FeS
Product
Fe: 1
S: 1
Which element is not balanced?
We balance an equation by adding Coefficients.
Coefficients are multipliers!
Fe + S2 → 2 FeS
Reactants
Fe: 1
S: 2
Product
Fe: 2
S: 2
If we add a coefficient of 2 to
the Products side
We now have 2 Fe and 2 S on
the Products side
Now which element is not balanced?
Where can we add
another coefficient that
would balance this
equation?
Fe + S2 → 2 FeS
Reactants
Fe:
S: 2
=
Product
Fe: 2
S: 2
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Let’s use coefficients to balance these chemical equations together:
___ H2O
→ ___ H2 + ___ O2
Reactant
Products
H
O
___ CH4 + ___ O2 → ___ CO2 + ___ H2O
Reactants
Products
C
H
O
___ Al + ___ CuCl2 → ___ Cu + ___ AlCl3
Reactants
Products
Al
Cu
Cl
___ NaCl + ___ AgNO3 → ___ NaNO3 + ___ AgCl
Reactants
Products
Na
Cl
Ag
NO3
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Five (5) Common Types of Chemical Reactions
Synthesis
Two or more reactants yield one product
Format:
A +
→ A
Example:
Fe + S
→ FeS
Decomposition (opposite of synthesis!) A one reactant yields two or more products
Format:
A
→ A +
FeS →
Example:
Fe + S
Single Replacement A single element (usually a metal) replaces another element in a compound
Both the reactants and the products consist of a single element plus a compound!
→
Format:
A +
C
Example:
Al + CuCl →
+ AC
Cu + AlCl
Double Replacement
The cation/metal (+) and anion/nonmetal (-) of two compounds “switch partners”
A compound + compound yields a compound + compound!
+
-
→ A+
Format:
A+ X- +
-
Example:
NaCl + AgF → NaF + AgCl
+
+ X-
Double Replacement reactions are the only type that are
NOT redox (oxidation - reduction) reactions!
Combustion
no really, burning stuff
A hydrocarbon (CxHx) reacts with oxygen (O2) to yield carbon dioxide (CO2) + water (H2O)
Format:
CxHx + O2 → CO2 + H2O
Example:
C4H10 + O2 → CO2 + H2O
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Predicting the Products of
Single and Double
Replacement Reactions
Single Replacement Reactions:
A single element replaces another in a compound
→
+
Format:
A
+ B
C
Example:
Al + CuCl3
+
→ B + A C
→ Cu + AlCl3
If you are just shown the reactants of a Single Replacement reaction like this:
Al + CuCl3
_________ + _________
What would you expect the products to be? Can you fill in the blanks?
Li +
NaBr →
_________ + _________
Fe + Cu(SO4) → _________ + _________
Double Replacement Reactions:
The cations (+) and anions (-) of two compounds “switch partners”
Format:
A+ X- + B+ Y-
Example:
NaCl + AgNO3
→ A+ Y- + B+ X→ NaNO3 + AgCl
If you are just shown the reactants of a Double Replacement reaction like this:
NaCl + AgNO3
_________ + _________
What would you expect the products to be? Can you fill in the blanks?
Na2CO3 + Sn(NO3)2
_________ + _________
Al2(SO4)3 + NaOH
_________ + _________
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Name__________________________
Oxidation/Reduction
UNIT
What is the charge of an electron? ________
Oxidation is the loss of electrons.
When negative electrons are lost, an atom becomes more positive (+)
Reduction is the gain of electrons. It is the reduction of charge!
When negative electrons are gained, an atom becomes more negative (-)
OIL RIG:
Oxidation
Is
Loss of electrons!
Reduction
Is
Gain of electrons!
A substance that has been oxidized has _______ negative electrons.
Therefore that substance has become more _______________.
Oxidation has nothing to do with oxygen!
A substance that has been reduced has _______ negative electrons.
Therefore that substance has become more ________________
It is the charge that is being reduced, not the number of electrons!
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An electron has a negative charge!
Oxidation
Is
Loss of electrons!
Reduction
Is
Gain of electrons!
Metallic elements Oxidize while Nonmetals Reduce
EXAMPLE:
reactants / before reaction
Charges:
0
4 Na(s)
0
+
O2 (g)
product / after reaction
+
-
2 Na2O(s)
In the above reaction; Na metal is neutral (0), the O2 molecule is neutral (0)
The product Na2O is neutral because it is made up of Na1+ cations and O2- anions
The Na went from being neutral before the reaction to becoming more positive after the reaction
To become more positive Na must have lost electrons (electrons are negative)
OIL = Oxidation Is Loss of electrons
Na is oxidized in the reaction!
The O went from being neutral before the reaction to becoming more negative after the reaction
To become more negative O must have gained electrons (electrons are still negative)
RIG = Reduction Is Gain of electrons
O is reduced in the reaction!
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Oxidation
Is
Loss of electrons!
Metals are Oxidized, Nonmetals are Reduced
Reduction
Is
Gain of electrons!
Magnesium (Mg) loses 2 electrons and becomes more positive.
OIL = Oxidation Is Loss of electrons.
Magnesium is oxidized in this reaction!
The nonmetal Sulfur (S) gains 2 electrons and becomes more negative.
RIG = Reduction Is Gain of electrons
Sulfur is reduced in this reaction!
The Photosynthesis Reaction
reactants / before reaction
+4 -2
+1
products / after reaction
-2
6 CO2 + 6 H2O
0
+1
-2
0
C6H12O6 + 6 O2
Carbon starts out positive and ends up neutral. Carbon got more negative (or less positive).
Carbon must have gained electrons (electrons are negative).
RIG = Reduction Is Gain of electrons
Carbon is reduced in this reaction!
Oxidation
Is
Loss of electrons!
Reduction
Is
Gain of electrons!
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