# Chemical Reactions

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```					Chemical Reactions

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

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
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?

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
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

organizer like the one below, ask a what or how question for
Properties and Changes of Matter
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

Chemical Reactions

End of Section:
Observing
Chemical
Change
Chemical Reactions

Noggin Knockers
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. (Just synthesis
reactions today)
Chemical Reactions

Conservation of Mass Demo (with 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     AB, which masses are equal?

1.   Mass of A = Mass of B
2.   Mass of B = Mass of AB
3.   Mass of A = Mass of AB
4.   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 - 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

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
Identify all of the following chemical equations that
represent a synthesis reaction:
1.   Mg + O2        2MgO
2.   AB      A+B
3.   A+B       AB
4.   A + BC        AC + B
5.   CuCl2 + Al        AlCl3 + Cu
Chemical Reactions

Noggin Knockers
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

Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of sodium metal
(Na) with oxygen gas (O2), forming sodium oxide (Na2O).
Chemical Reactions

Balancing Chemical Equations for Synthesis
Reactions (Describe the 1st one in words & include
the number of each atom or molecule)
Na +   Cl2        NaCl

P +    Cl2         PCl3

N2 +    H2        NH3
Chemical Reactions

Noggin Knockers
Chemical Reactions

Learning Objectives
1. Apply the principle of the conservation of mass (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. Just
decomposition today!
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         Hg +      O2

2.        KClO3        KCl +         O2

3.        NaHCO3         Na2CO3 +         H 2O +   CO2
Chemical Reactions

How can you tell if a chemical reaction is a
decomposition reaction?
A.   If there’s 2 or more products.
B.   If there’s 2 or more reactants.
C.   If there’s only 1 reactant.
D.   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.   A+B     AB
B.   AB     A+B
C.   AB + C    AC + B
D.   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.   2H2O + O2     2H2O2
B.   2H2O2     2H2O + O2
C.   H2O2     H2O + O2
D.   H2O + O2     H2O2
Chemical Reactions

Single Replacement Reactions
Goals: Observe and write the balanced chemical equations
for 3 single replacement reactions (from the experiment,
demo, and video), and identify this type of reaction.

Procedure: Clean the nail with a paper towel, then 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 all 3
reactions (including one from the demo and one from the
video) and describe the characteristics of a single
replacement reaction.
Chemical Reactions

Balancing Equations
Experiment:

Demo:

Video:
Chemical Reactions

Single Replacement Reaction
One element (or type of atom) replaces another in a
compound.
XY + Z       XZ + Y
Analogy:
Chemical Reactions

For a single replacement reaction…
A.   Two types 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 single
replacement reaction?
A.   AB     A+B
B.   AB + CD   AD + BC
C.   AB + C   AC + B
D.   A+B     AB
Chemical Reactions

Which of following only shows copper (Cu) being
replaced by silver (Ag)?
A.   2Ag + CuSO4      Ag2SO4 + Cu
B.   Ag + Cu    AgCu
C.   CuCl2    Cu + Cl2
D.   CuSO4 + 2AgNO3     Cu(NO3)2 + Ag2SO4
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 +     NaCl

Na2SiO3 +   CuSO4    CuSiO3 +        Na2SO4

Na2SiO3 +   NiCl2   NiSiO3 +        NaCl

Na2SiO3 +   CoCl2    CoSiO3 +       NaCl
Chemical Reactions

Double Replacement Reaction (Video)
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

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.   AB     A+B
B.   AB + CD   AD + BC
C.   AB + C   AC + B
D.   A+B     AB
Chemical Reactions

Which of the following is a double replacement
reaction?
A.   2Ag + CuSO4      Ag2SO4 + Cu
B.   Ag + Cu    AgCu
C.   CuCl2    Cu + Cl2
D.   CuSO4 + 2AgNO3     Cu(NO3)2 + Ag2SO4
Chemical Reactions

For a single replacement reaction…
A.   Two types 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 single
replacement reaction?
A.   AB     A+B
B.   AB + CD   AD + BC
C.   AB + C   AC + B
D.   A+B     AB
Chemical Reactions

Which of following only shows copper (Cu) being
replaced by silver (Ag)?
A.   2Ag + CuSO4      Ag2SO4 + Cu
B.   Ag + Cu    AgCu
C.   CuCl2    Cu + Cl2
D.   CuSO4 + 2AgNO3     Cu(NO3)2 + Ag2SO4
Chemical Reactions

Combustion Reactions (Balance for Extra Credit)
Film Canister Rocket (Combustion of methanol):

CH4O + O2       CO2 + H2O

Ping Pong Popper (Combustion of ethanol):

C2H6O + O2      CO2 + H2O

Whoosh Bottle (Combustion of Isopropyl alcohol):

C3H8O + O2      CO2 + H2O
Chemical Reactions - Describing Chemical Reactions

Building Vocabulary
Using a word in a sentence helps you think about how best
paragraphs that contain definitions of Key Terms. Use the
information you have learned to write a meaningful sentence
using each Key Term.
Key Terms:               Examples:
chemical equation
closed system           A chemical system, matter is not allowed to enter or
In a closed equation is a short, easy way to show a
replacement             Replacement is the process in which one element
chemical reaction.
leave.
replaces another in a compound or two elements in
reactant
coefficient               substance is number places.
different compounds trade in beginning equation
A coefficientyouahave at the a chemicalof a reaction is
a reactant.
telling you how many atoms or molecules of a reactant
product                 ornew substance produced in a reaction is a product.
A product take part in the reaction.
synthesis
conservation of mass    Synthesis means combining two or more a chemical
Conservation of mass means that duringelements or
compounds to make a more complex substance.
reaction, matter is not 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
Describe how the following affect the rate of a chemical
reaction…
•Temperature

•Surface Area

•Using a catalyst

•Using an inhibitor

•Concentration
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 - 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

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       4Fe + 3CO2

5- 2SO2 + O2       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
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.
3. Baking soda can be used to put out small fires.
Chemical Reactions - Fire and Fire Safety

Chemical Reactions

End of Section:
Fire and Fire
Safety
Chemical Reactions

Graphic Organizer
Chemical
reactions

can be                are written as

Endothermic            Exothermic
reactions                                    Equations
reactions
balanced with

which require                      written using           Coefficients

Activation
energy               Chemical                 Arrows and
symbols                  plus signs
Chemical Reactions

End of Section:
Graphic Organizer

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