Chemical Reactions
Table of Contents
Observing Chemical Change
Describing Chemical Reactions
Controlling Chemical Reactions
Fire and Fire Safety
Chemical Reactions - Observing Chemical Change
Properties and Changes in Matter
Matter can undergo both physical change and
chemical change.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
A student places two substances
in a flask and measures the
temperature once per minute
while the substances react. The
student plots the time and
temperature data and creates
the graph at left.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Reading Graphs:
What was the temperature in
the flask at 4 minutes? When
was the first time the
temperature was at 6ºC?
At 4 minutes the temperature
in the flask was about 23ºC.
The first time the temperature
was 6ºC was at about 7
minutes.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Calculating:
How many degrees did the
temperature drop between
2 minutes and 5 minutes?
20ºC
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Interpreting Data:
Is the reaction endothermic or
exothermic? Explain.
The reaction was
endothermic; it absorbed
thermal energy from the
reaction mixture, causing the
temperature to drop.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Inferring:
At what temperature did the
reaction stop? How can you
tell?
The reaction stopped at about
2ºC. You can tell because that
is the lowest temperature
reached.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Drawing Conclusions:
Suppose the temperature in
the flask increased instead of
decreased as the reaction
occurred. In terms of energy,
what kind of reaction would it
be? Explain.
If the temperature increased,
the reaction would be
exothermic; an exothermic
reaction is one in which
energy is released.
Chemical Reactions - Observing Chemical Change
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a what or how question for
each heading. As you read, write answers to your questions.
Properties and Changes of Matter
Question
Answer
What are physical
Physical properties are
properties of matter?
characteristics that can be
observed without changing
one substance into another.
What is the evidence for
The evidence for chemical
chemical reactions?
reactions is the formation of
new substances and
changes in energy.
Chemical Reactions - Observing Chemical Change
Links on Chemical Changes
Click the SciLinks button for links on chemical changes.
Chemical Reactions
End of Section:
Observing
Chemical
Change
Chemical Reactions
Learning Objectives
1. Apply the principle of the conservation of mass to chemical
reactions (in other words, balance chemical equations
correctly).
2. Identify what a chemical equation contains (with an example).
3. Explain what a balanced chemical equation must show.
4. Identify the 4 main types of chemical reactions. (Synthesis
tomorrow)
Chemical Reactions
Conservation of Mass Demo (NO Lab Write-up)
Goal- Determine if mass was conserved (remained constant)
for the reaction of copper (II) sulfate with sodium hydroxide
to form copper (II) hydroxide: Cu(OH)2.
Data: Mass before = ?
Mass After = ?
Conclusion: Was mass conserved? How do you know?
Chemical Reactions - Describing Chemical Reactions
Conservation of Mass
The principle of conservation of mass states that in a
chemical reaction, the total mass of the reactants must
equal the total mass of the products. This is why we must
balance chemical equations (because mass is conserved)!
Chemical Reactions
Conservation of Mass Review
For the reaction A + B
1.
2.
3.
4.
AB, which masses are equal?
Mass of A = Mass of B
Mass of B = Mass of AB
Mass of A = Mass of AB
Mass of A + Mass of B = Mass of AB
Chemical Reactions - Observing Chemical Change
Properties and Changes in Matter
Chemical reactions occur when bonds break and new bonds
form.
Chemical Reactions - Describing Chemical Reactions
Describing Chemical Reactions
Cellular phone messages make use of symbols and
abbreviations to express ideas in shorter form. Similarly,
chemists often use chemical equations in place of words.
Chemical Reactions - Describing Chemical Reactions
What Are Chemical Equations?
Chemical equations use chemical formulas and other
symbols instead of words to summarize a reaction.
Chemical Reactions - Describing Chemical Reactions
Chemical Formulas
The formula of a compound identifies
the elements in the compound and the
ratios in which their atoms are present.
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
Magnesium metal (Mg) reacts
with oxygen gas (O2), forming
magnesium oxide (MgO). To
write a balanced equation for
this reaction, first write the
equation using the formulas of
the reactants and products, then
count the number of atoms of
each element.
Chemical Reactions
Balancing Chemical Equations
Mg
+
O2
MgO
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation (due to the principle of the conservation of
matter).
Chemical Reactions
Balancing Equations Practice
K
+
Na +
I2
KI
H 2O
NaOH +
AgNO3 +
K 2S
CuSO4 +
NaOH
H2
KNO3 +
Na2SO4 +
Ag2S
Cu(OH)2
Chemical Reactions
Noggin Knockers
Chemical Reactions
Synthesis Reaction Experiment
Goals: Observe and write the balanced chemical equations for 2
synthesis reactions, and identify a synthesis reaction.
Procedure: Given verbally. Do NOT touch the penny, tongs, or
burner after heating! Only put a pre-1982 penny in the flame!
Results: Observations of the penny after heating (but before you
place it in the water) and after placing the penny in the water.
Conclusion: Write the balanced equations for both reactions and
describe the characteristics of a synthesis reaction. (Products: Red
= Cu2O, Dull black = CuO)
Chemical Reactions
Synthesis Reaction
Multiple (more than 1) reactants
combining to form 1 product.
Example: Copper metal combining
with oxygen gas to form copper (II)
oxide…
2Cu + O2
2CuO
Chemical Reactions
Synthesis Reaction Review
1.
2.
3.
4.
5.
Identify all of the following chemical equations that
represent a synthesis reaction:
Mg + O2
2MgO
AB
A+B
A+B
AB
A + BC
AC + B
CuCl2 + Al
AlCl3 + Cu
Chemical Reactions
Balancing Chemical Equations for Synthesis
Reactions
Na +
Cl2
NaCl
Balance the equation for the reaction of sodium metal (Na) with oxygen gas
(O2), forming sodium oxide (Na2O).
P +
N2 +
Cl2
H2
PCl3
NH3
Chemical Reactions
Ratios in Chemical Equations
+
Energy
There’s a 2 to 1 ratio of hydrogen gas (H2) to oxygen gas (O2) that
produces 2 water molecules (H2O).
What’s the ratio of oxygen gas (O2) to water (H2O)?
1 to 2
Chemical Reactions
Noggin Knockers
Chemical Reactions
Decomposition Reactions
Goals: Observe and write the balanced chemical equations
for 2 decomposition reactions (one from the demo), and
identify this type of reaction.
Procedure: Heat up a piece of chalk (CaCO3) in the burner
flame for at least 5 minutes. Then place the chalk in the cup
with water and observe what happens.
Results: Observations of the chalk after heating (but before
you place it in the water) and after placing the chalk in the
water.
Conclusions: Write the balanced equations for both
reactions (one is from the demo) and describe the
characteristics of a decomposition reaction.
Chemical Reactions
Balancing Equations (Decomposition Reactions)
Chemical Reactions
Decomposition Reactions
Only 1 reactant, but
multiple products
(more than 1).
XY
X+Y
Chemical Reactions
Balancing Chemical Equations (Decomposition):
Describe the last one in words & include the
number of each molecule- Ion chart on p. 23
1.
HgO
2.
KClO3
3.
NaHCO3
Hg +
O2
KCl +
Na2CO3 +
O2
H 2O +
CO2
Chemical Reactions
Noggin Knockers
Chemical Reactions
Single Replacement Reactions
Goals: Observe and write the balanced chemical equations
for 3 single replacement reactions (3 from the demos), and
identify this type of reaction.
Procedure: Place the iron nail into the blue solution of
copper (II) sulfate. Take it out after a few seconds.
Results: Observations of the nail before and after placing it
in the copper (II) sulfate solution.
Conclusions: Write the balanced equations for BOTH
reactions (including the one from the demo) and describe the
characteristics of a single replacement reaction.
Chemical Reactions
Balancing Equations
Demo 1:
Demo 2:
Chemical Reactions
Balancing Equations
Demo 3 (Thermite):
Chemical Reactions
Single Replacement Reaction
One element (or type of atom) replaces another in a
compound.
XY + Z
XZ + Y
Analogy:
Chemical Reactions
Noggin Knockers
Chemical Reactions
Double Replacement Reactions
Goals: Observe and write the balanced chemical equations for 6 double
replacement reactions (5 from the lab and 1 from the video), and identify this
type of reaction.
Procedure: Place 3-5 drops of the following solutions in their own well (in the
chem. plate): Magnesium sulfate (MgSO4), Nickel chloride (NiCl2), Copper (II)
sulfate (CuSO4), Iron (III) chloride (FeCl3), & Cobalt chloride (CoCl2). Then
add 3-5 drops of the sodium silicate solution (Na2SiO3) to form metal silicates
and stir with the clean end of a toothpick. Disposal- scoop out solids and put
them in the trash and wipe the plate clean. WASH hands immediately if you get
any chemical on them!
Results: Observations of each reaction in terms of what formed. You may want
to write down your observations under the chemical formula for the compound
that formed in the equation for each reaction.
Example: Al2(SiO3)3
white
Conclusions: Write the balanced equations for all reactions (including one from
the video) and describe the characteristics of a double replacement reaction.
Chemical Reactions
Balancing Equations (Silicate ion = SiO3-2)
Na2SiO3 +
MgSO4
MgSiO3 +
Na2SO4
Na2SiO3 +
FeCl3
Fe2(SiO3)3 +
Na2SiO3 +
CuSO4
CuSiO3 +
Na2SiO3 +
NiCl2
NiSiO3 +
NaCl
Na2SiO3 +
CoCl2
CoSiO3 +
NaCl
NaCl
Na2SO4
Chemical Reactions - Describing Chemical Reactions
Classifying Chemical Reactions
Double Replacement reactions involve 2 types of atoms (or
groups of atoms) switching places in different compounds.
AB + CD
AD + BC
Chemical Reactions
Double Replacement Reaction (Video)
Chemical Reactions
Balancing Equations (Silicate ion = SiO3-2)
Na2SiO3 +
MgSO4
MgSiO3 +
Na2SO4
Na2SiO3 +
FeCl3
Fe2(SiO3)3 +
Na2SiO3 +
CuSO4
CuSiO3 +
Na2SiO3 +
NiCl2
NiSiO3 +
NaCl
Na2SiO3 +
CoCl2
CoSiO3 +
NaCl
NaCl
Na2SO4
Chemical Reactions
For a single replacement reaction…
A.
B.
C.
D.
Two types of atoms switch places between compounds.
One type of atom replaces another in a compound.
There are always 2 reactants and 1 product.
There is only one reactant.
Chemical Reactions
Which of the following represents a single
replacement reaction?
A.
B.
C.
D.
AB
A+B
AB + CD
AD + BC
AB + C
AC + B
A+B
AB
Chemical Reactions
Which of following only shows copper (Cu) being
replaced by silver (Ag)?
A.
B.
C.
D.
2Ag + CuSO4
Ag2SO4 + Cu
Ag + Cu
AgCu
CuCl2
Cu + Cl2
CuSO4 + 2AgNO3
Cu(NO3)2 + Ag2SO4
Chemical Reactions
How can you tell if a chemical reaction is a
decomposition reaction?
A.
B.
C.
D.
If there’s 2 or more products.
If there’s 2 or more reactants.
If there’s only 1 reactant.
If there’s only 1 product.
Chemical Reactions
Why are synthesis and decomposition reactions
considered opposites?
A. They both have only one reactant.
B. Synthesis reactions have 2 products while decomposition
reactions have only 1 product.
C. They’re not opposites.
D. Synthesis reactions have only 1 product while
decomposition reactions have only 1 reactant.
Chemical Reactions
Which of the following represents a decomposition
reaction?
A.
B.
C.
D.
A+B
AB
AB
A+B
AB + C
AC + B
AB + CD
AD + BC
Chemical Reactions
Which of the following shows 2 molecules of
hydrogen peroxide (H2O2) breaking down into 2
molecules of water and 1 molecule of oxygen gas
(O2)?
A.
B.
C.
D.
2H2O + O2
2H2O2
2H2O2
2H2O + O2
H2O2
H2O + O2
H2O + O2
H2O2
Chemical Reactions
For a double replacement reaction…
A. Two types of atoms or groups of atoms switch places
between compounds.
B. One type of atom replaces another in a compound.
C. There are always 2 reactants and 1 product.
D. There is only one reactant.
Chemical Reactions
Which of the following represents a double
replacement reaction?
A.
B.
C.
D.
AB
A+B
AB + CD
AD + BC
AB + C
AC + B
A+B
AB
Chemical Reactions
Which of the following is a double replacement
reaction?
A.
B.
C.
D.
2Ag + CuSO4
Ag2SO4 + Cu
Ag + Cu
AgCu
CuCl2
Cu + Cl2
CuSO4 + 2AgNO3
Cu(NO3)2 + Ag2SO4
Chemical Reactions
Math
Chemical Reactions
Math
Chemical Reactions
Noggin Knockers
Chemical Reactions
Combustion Reactions (Balance for Extra Credit on Test)
Film Canister Rocket (Combustion of methanol):
CH4O + O2
CO2 + H2O
Ping Pong Popper (Combustion of ethanol):
C2H6O + O2
CO2 + H2O
Whoosh Bottle (Combustion of 2-propanol AKA isopropyl
alcohol):
C3H8O + O2
CO2 + H2O
Chemical Reactions
Homework- p. 63: 1a, 2b, 3a, 3b, 3c, 4, & 5
1a- Formulas- number of each type of atom, arrow means “yields”
or “produces”. Plus sign- what’s reacting together and/or what 2
substances are produced because they separate the substances in
the equation.
2b- 250 g (Mass of reactants = Mass of the products)
3a- Synthesis, Decomposition, Replacement (Single & Double)
3b- 2 products minimum
3c- Synthesis (1 product)
4- 2Fe2O3 + 3C
5- 2SO2 + O2
4Fe + 3CO2
2SO3
Chemical Reactions
Practice Problems
Chemical Reactions - Describing Chemical Reactions
Building Vocabulary
Using a word in a sentence helps you think about how best
to explain the word. After you read the section, reread the
paragraphs that contain definitions of Key Terms. Use the
information you have learned to write a meaningful sentence
using each Key Term.
Key Terms:
closed system
chemical
equation
replacement
reactant
coefficient
product
Examples:
In chemical
A
a closed system,
equationmatter
is a short,
is noteasy
allowed
way to
to enter
show or
a
Replacement is the process in which one element
chemical reaction.
leave.
replaces another in a compound or two elements in
substance
you
at the
a reaction is
A coefficient
is ahave
number
in
abeginning
chemicalofequation
different
compounds
trade
places.
a reactant.
telling
you how many atoms or molecules of a reactant
or
product
take part
in the reaction.
A new
substance
produced
in a reaction is a product.
synthesis
conservation of mass
Synthesis
means
combining
two
or during
more elements
or
Conservation
of mass
means
that
a chemical
compounds
to make
more complex
substance.
reaction, matter
is nota created
or destroyed.
open system
decomposition
In an open system,
matter
can enter
from
or escape
Decomposition
means
breaking
down
compounds
to the
surroundings.
into
simpler
products.
Chemical Reactions
End of Section:
Describing
Chemical
Reactions
Chemical Reactions
Learning Objective (Pg. 19 of note packet)
Describe how the following affect the rate of a chemical
reaction…
•Temperature
•Using a catalyst
•Surface Area
•Using an inhibitor
•Concentration
Chemical Reactions - Controlling Chemical Reactions
Rates of Chemical Reactions
The cells in your body (as in all living
things) contain biological catalysts called
enzymes. At the end of a reaction, an
enzyme molecule is unchanged.
Chemical Reactions - Controlling Chemical Reactions
Energy and Reactions
All chemical reactions need a certain amount of activation
energy to get things started.
Chemical Reactions - Controlling Chemical Reactions
Energy and Reactions
Both exothermic and endothermic reactions need energy
to get started.
Chemical Reactions - Controlling Chemical Reactions
Relating Cause and Effect
As you read, identify the factors that can cause the rate of a
chemical reaction to increase. Write the information in a
graphic organizer like the one below.
Causes
Increase in surface area
Effect
Increase in temperature
Increased rate of reaction
Increase in concentration
of reactants
Use of a catalyst
Chemical Reactions
Homework- p. 63: 1a, 2b, 3a, 3b, 3c, 4, & 5
1a- Formulas- number of each type of atom, arrow means “yields”
or “produces”. Plus sign- what’s reacting together and/or what 2
substances are produced b/c they separate the substances in the
equation.
2b- 250 g (Mass of reactants = Mass of the products)
3a- Synthesis, Decomposition, Replacement (Single & Double)
3b- 2 products minimum
3c- Synthesis (1 product)
4- 2Fe2O3 + 3C
5- 2SO2 + O2
4Fe + 3CO2
2SO3
Chemical Reactions
Homework- p. 71: 2a
2a- Speed up a reaction- increase temperature, increase
surface area, increase concentration of the reactants, or add
a catalyst; slow down a reaction- decrease temperature,
decrease surface area, decrease concentration of the
reactants; add an inhibitor.
Chemical Reactions
Data Sharing Lab
Click the PHSchool.com button for an activity about sharing
data for the Skills Lab Temperature and Enzyme Activity.
Chemical Reactions - Controlling Chemical Reactions
Exothermic and Endothermic Reactions
Click the Video button to watch a movie about exothermic
and endothermic reactions.
Chemical Reactions
End of Section:
Controlling
Chemical
Reactions
Chemical Reactions - Fire and Fire Safety
Understanding Fire
Three things are necessary to
start and maintain a fire–fuel,
oxygen, and heat.
Chemical Reactions - Fire and Fire Safety
Understanding Fire
The fire triangle can be controlled
in the grill. If any part of the fire
triangle is missing, the fire will
not continue.
Chemical Reactions - Fire and Fire Safety
Home Fire Safety
If you know how to
prevent fires in your
home and what to do
if a fire starts, you are
better prepared to
take action.
Chemical Reactions - Fire and Fire Safety
Using Prior Knowledge
Before you read, write what you know about fire safety in a
graphic organizer like the one below. As you read, write what
you learn.
What You Know
1. A fire needs fuel to burn.
2. A fire need oxygen to burn.
3. All homes should have smoke detectors.
What You Learned
1. Fire is a result of a combustion reaction.
2. The most deadly fires start with cigarettes.
3. Baking soda can be used to put out small fires.
Chemical Reactions - Fire and Fire Safety
Links on Fire Safety
Click the SciLinks button for links on fire safety.
Chemical Reactions
End of Section:
Fire and Fire
Safety
Chemical Reactions
Graphic Organizer
Chemical
reactions
can be
Endothermic
reactions
are written as
Exothermic
reactions
Equations
balanced with
which require
Activation
energy
written using
Chemical
symbols
Coefficients
Arrows and
plus signs
Chemical Reactions
End of Section:
Graphic Organizer