Do Now
CHEMICAL REACTIONS
• What are some signs that a chemical
change may have taken place?
• Where are the reactants and products in a
reaction? What do they represent?
• Describe the law of conservation of mass.
Chemical Reaction
Chemical Reaction
• A process in which one or more
substances are converted into new
substances with different chemical and
physical properties.
properties
• In chemical reactions, existing bonds are
broken, atoms are rearranged, and new
bonds are formed.
• Reactant: substances that enter the
reaction (start)
• Product: substances that come out of
reaction (end)
Evidence
Chemical Equations
• How do we know that a reaction has taken
place?
• Represent reactions with symbols and
formulas, tells us the identities and relative
amounts of reactants and products in a
chemical reaction
reaction.
– Production or absorption of energy (heat and
light)
– Production of a gas
– Formation of a precipitate (a solid that forms
as a result of mixing 2 solutions).
– Color change
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Word Equations
• Give names of reactants and products
+ = “reacts with,” “add,” or “ added to”
→ = “yields” or “produces”
• Describe the following as a word equation:
Calcium + Oxygen → Calcium Oxide
Formula Equations
• Give symbols or formulas of reactants and
products
• When going from word to formula, be
careful to use the correct formulas.
formulas
(Remember the diatomic molecules Br2, I2,
N2, Cl2, H2, O2, F2)
• Write the formula for the previous word
equation:
• Ca + O2 → CaO
Additional symbols in equations:
• (s) or ↓ = Solid
• (l) = Liquid
• Write the word equation for the reaction
that occurs when solid sodium oxide is
added to water and forms sodium
hydroxide (dissolved in water).
water)
• (g) or ↑ = Gas
• (aq) = Aqueous (dissolved in water)
• Na2O(s) + H2O → NaOH (aq)
Names of Acids
• Write the word equation and formula for
methane reacting with oxygen to produce
carbon dioxide and water.
• Chemistry Reference Table K lists the
common acids you need to use
Methane + oxygen Æ carbon dioxide + water
CH4 + O2 Æ CO2 + H2O
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LAW OF CONSERVATION OF
MATTER (MASS)
Law of Conservation of Mass
Mass is neither created nor
destroyed during chemical
or physical reactions.
• Formula equations must be written in
accordance with the LAW OF
CONSERVATION OF MATTER (MASS) =
atoms cannot be created or destroyed in a
chemical reaction. They can only be
rearranged!
Total mass of reactants = Total mass of products
Formula equations must be written in
accordance with the LAW OF
CONSERVATION OF MATTER (MASS)
Antoine Lavoisier
Law of Conservation of Mass
• The same number and kind of atoms must
appear on both sides of the arrow!!!
• COEFFICIENTS= small whole numbers
that appear in front of a formula in a
chemical equation.
• The coefficient multiplies the number of
atoms of each element in the formula that
follows.
Trial and Error is the best way
to balance equations.
Steps to Writing Balanced Equations:
1. Read the word equation that describes a
reaction:
zinc + hydrochloric acid → zinc chloride + hydrogen
2. Replace the words with symbols.
Zn +HCl → ZnCl2 + H2
– Ex: 2 H2O = 4 H and 2 O
• 3. Count the number of atoms on each
side of the arrow. (Keep polyatomic ions
that exist on both sides of the equation as
one!)
Zn +HCl → ZnCl2 + H2
1 Zn
1 Zn
1H
2H
1 Cl
2 Cl
• 4. Balance using trial and error.
Zn +2HCl → ZnCl2 + H2
• 5. Check
1 Zn
2H
2 Cl
1 Zn
2H
2 Cl
3
Practice
• Na + H2O Æ NaOH + H2
1 Na
1 Na
2H
3H
1O
1O
• 2Na + 2H2O Æ 2NaOH + H2
2 Na
2 Na
4H
4H
2O
2O
Practice
• Iron (III) oxide and hydrogen are the
reactants. Iron and Water are the
products. Find the balanced equation.
Fe2O3 + H2 Æ Fe + H2O
2 Fe
1 Fe
3O
1O
2H
2H
Practice
Fe2O3 + H2 Æ Fe + H2O
2 Fe
1 Fe
3O
1O
2H
2H
Fe2O3 + 3H2 Æ 2Fe + 3H2O
2 Fe
2 Fe
3O
3O
6H
6H
TYPES OF CHEMICAL
REACTIONS
• Thousands of chemical reactions occur in
nature. Reactions can be classified into
one of several categories. Classification is
important for predicting products of
reactions.
– 1. SYNTHESIS REACTIONS
– 2. DECOMPOSITION REACTIONS
– 3. COMBUSTION
– 4. SINGLE REPLACEMENT REACTIONS
– 5. DOUBLE REPLACEMENT REACTIONS
Review
• What do you notice about the arrangement
of elements in the reactants and products?
• 2Al + Fe2O3 Æ 2Fe + Al2O3
• HCl + N
NaOH
OH Æ H2O + NaCl
N Cl
SYNTHESIS
DECOMPOSITION
SINGLE
REPLACEMENT
DOUBLE
REPLACEMENT
COMBUSTION
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1. SYNTHESIS REACTIONS
2. DECOMPOSITION REACTIONS
• Two or more substances combine to form
a new compound (composition or direct
combination).
• Examples:
• A + X → AX
• 2 Mg +O2 → 2 MgO
• 2 CO + O2 → 2 CO2 (car exhaust)
• CO2 + H2O Æ H2CO3 (carbonic acid)
• A single compound undergoes a reaction
that produces two or more simpler
substances (breakdown).
• Examples:
• AX → A + X
• 2 H2O2(l) → 2 H2O(l) +O2(g)
• 2 H2O(l) → 2 H2(g) +O2(g)
Electrolysis of Water
– Electrolysis- the decomposition of a
substance by applying an electric current.
3. COMBUSTION REACTIONS
• A substance combines with oxygen (O2) to
release large amounts of energy in the
form of light and heat.
• CH4 +O2 → CO2 +2H2O
http://www.chem.uiuc.edu/clcwebsite/meth.html
Writing Chemical Reactions
From Particle Diagrams
• Chemical formulas can be written from
diagrams as well
• Just like word problems, you must look at
your reactants and products as well as
balance the equation
• Write the chemical reaction for the
following diagram:
Key:
= Atom of element X
= Atom of element C
Reactants
Products
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SYNTHESIS
DECOMPOSITION
SINGLE
REPLACEMENT
Single and Double
Replacement
p
Reactions
DOUBLE
REPLACEMENT
COMBUSTION
4. SINGLE REPLACEMENT
REACTIONS
• One element replaces a similar element in
a compound (displacement).
• A + BX → B + AX
• Mg
M (s) + 2HCl(aq) → MgCl
M Cl2(aq) + H2 ↑
• 2Al(s)+3Pb(NO3)2(aq) → 2Al(NO3)3(aq)+3Pb(s)
• This type of reaction occurs only under
certain conditions!
What does “certain conditions”
mean?
• A + BX → B + AX
•
•
•
•
•
A (metal or nonmetal)
B (metal)
X (nonmetal)
Metals can only switch with Metals
Nonmetals can only switch with Nonmetals
Using the Activity Series
(Table J)
• Some elements are considered to be very
reactive, some are considered unreactive.
The ability of an element to react is called
the element’s
element s “activity
activity.”
• Higher metals are more reactive than
lower metals. A metal will only replace
another metal in a compound if it is
HIGHER on Table J.
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Using the Activity Series
• Metals: the higher the activity, the greater
its tendency is to lose electrons and
therefore more reactive.
• Nonmetals: the higher the reactivity, the
greater its tendency to gain electrons and
therefore more reactive.
• The activity series is used to predict
whether or not a chemical reaction will
occur (single replacement reactions).
• If it is lower no reaction (NR) will occur!
Identify METALS: Will a Singlereplacement reaction occur?
• If the single element is further up on the
activity chart (Table J) the reaction will
occur.
• For example:
• Al + CuCl2 → AlCl3 + Cu
Using the Activity Series
• Single Replacement reactions only occur
when an element is more reactive (higher
on table J) than the element being
replaced.
replaced
In each of the following, circle
which metal is more active:
• 1. Li or Al
• 2. Au or Mg
• 3. Na or Pb
In each of the following, predict
whether there will be a reaction,
then balance the reactions:
• Mg + CuSO4 →
• Al + LiCl →
Identify NONMETALS: Will a
Single-replacement reaction occur?
• If the single element is higher up on table
J, then the reaction will occur!
• For example:
• F2 + 2LiBr
2LiB → B
Br2 + 2LiF
• Sn + Ba3PO4 →
7
In each of the following, circle
which nonmetal is more active:
• 4.
F2 or I2
• 5.
Br2 or Cl2
• 6.
Cl2 or I2
Rules for completing and writing
single replacement reactions.
1. Determine whether the reaction will occur or not
Li + CuSO4 →
Yes a reaction will occur (Lithium is higher up on the
chart)
2 D
2.
Determine
t
i th
the products
d t off th
the reaction
ti b
by switching
it hi the
th
appropriate elements.
Li +CuSO4 → LiSO4 + Cu
3. Place the charges on the elements and balance each of
the new compounds formed.
Li + CuSO4 → Li2(SO4) + Cu
4. Balance the entire equation.
2 Li + CuSO4 → Li2(SO4) + Cu
In each of the following, predict
whether there will be a reaction,
then balance the reactions:
• I2 + NaF →
• F2 + MgBr2 →
• Cl2 + BaI2 →
Practice Completing SingleReplacement Reactions
1. Cu + Ag(NO3) Æ
2. Fe + Cu(NO3)2 Æ
3. Ca + H2O Æ
4. Zn + NaCl Æ
5. DOUBLE REPLACEMENT
REACTIONS
Conditions when Double
Replacement Reactions occur
• The ions of 2 compounds exchange
places in an AQUEOUS solution to form 2
new compounds.
• Examples:
• AB + CD → AD + CB
• Pb(NO3)2(aq) +KI(aq) → KNO3(aq) + PbI2(s)
• Double replacement reactions do not
always occur.
• We use the term No Reaction (NR) when
no significant change occurs in a reaction.
• 1. If the product is insoluble. (A precipitate
is formed) ↓
– Insoluble: cannot be dissolved in water
– Precipitate: an insoluble product
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Solubility Chart (Table F)
Determine whether the compound is soluble or insoluble
a. NH4OH
b. PbCl2
c. BaCO3
d. Al(OH)3
e. Na2S
f. K2SO4
g. CaSO4
h. Mg3(PO4)2
i. Zn(OH)2
Now complete each of the following double replacement equations. For each of the products use Table F to assign a notation of (s) or (aq) below each formula.
1. BaCl2 (aq) + Na2CO3 (aq) →
3. CaI2 (aq) + Na3PO4 (aq) →
2. Zn(NO3)2 (aq) + KOH (aq) →
4. CuSO4 (aq) + (NH4)2CO3 (aq) →
Type of reaction
Definition
Example
Synthesis
Two or more substances combine to form a new compound.
2Mg + O2→ 2MgO
Decomposition
A single compound undergoes a reaction that produces two or more simpler substances (breakdown).
H2O2(l) → 2H2O(l) + O2 (g)
Single Replacement
One element replaces a similar element in a compound.
Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)
Double Replacement
The ions of 2 compounds exchange places in an AQUEOUS
solution to form 2 new compounds. The metals in the compounds switch places.
2 Li + CuSO4 → Li2(SO4) + Cu
A substance combines with oxygen (O2) to release large amounts of energy in the form of light and heat.
CH4 +O2 → CO2 +2H2O
Combustion Reaction
When will the reaction take place
•Single Replacement reactions only take occur when one element is more active than the element being replaced.
•Use Table J Activity Series
•Metals replace metals in a compound.
Nonmetals replace nonmetals in a replace nonmetals in a
•Nonmetals
compound.
1. If the product is insoluble. (A precipitate is formed) ↓
2. If water is a product
3. If the product decomposes into a gas. ↑
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