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8th Science
• molecule – combination of 2 or more atoms
bonded together
• compounds – substance made of 2 or more
elements chemically combined
• synthesis – 2 or more substances
combined to make a more complex
substance
• decomposition – breaking down of
compounds into simpler products
• replacement – when element (s) in a
compound (s) trade places
• Signs of a chemical reaction
•
•
•
•
•
Color change
Odor
Precipitate formation
Release of a gas
Energy change
• Exothermic reaction – heat given off
• Endothermic reaction – heat taken in
• Reaction needs
energy to begin
• Once energy
available atoms
begin forming new
bonds
• Minimum amt.
needed is
activation energy
• If exothermic additional energy
not needed to keep
going as energy is
being given off
• If endothermic need constant
supply of energy to
keep going as
energy is being
absorbed
• Reactions don’t all happen at the
same rate
• Speed can depend on conditions and
how easily particles can get
together
• Reaction can be controlled by
concentration, temperature, surface
area and using catalysts or
inhibitors
• Increase
concentration
• Makes more
particles available
to react
• Increase
temperature
• Heat makes
particles move
faster or
particles come
in contact more
often due to
more movement
• Change activation
rate by adding
catalyst
• Allows need for less
energy to make
reaction happen
• Catalyst not
considered part of
reaction
• In humans have
enzymes to allow
reaction to occur at
a lower temperature
• Break material into
smaller pieces
more area exposed
for reaction to
occur faster
• Inhibitor used to
slow down reaction
• Work in many
different ways
• Reactions classified by what
happens to reactants and products
• May add together, break apart, or
exchange parts
• Major types called combination,
decomposition, or replacement
• Can tell type by the chemical
equation
•
Example – sulfur
trioxide and water
to form sulfuric acid
• SO2 + H2O
H2SO4
• Reaction in which 2
or more substances
combine to form a
single product,
reactants may be
elements or
compounds, but
product is always a
single compound
• Reaction in which single substance breaks down
into 2 or more simpler substances, always just a
single reactant in a decomposition
• Example – breakdown of calcium carbonate upon
heating
•
CaCO3 + heat
CaO + CO2
Zn + 2HCl
ZnCl2 + H2
• Reactions in which
an element within
a compound is
displaced by a
separate element,
always has 2
reactants, one of
which is always an
element
• Reaction in which
positive ion from one
ionic compound
exchanges with
positive ion of another
ionic compound,
always have 2
compounds for
reactants, usually
occurs in aqueous
solution and results in
either formation of a
precipitate, production
of a gas, or formation
of a molecular
compound such as
water
AgNO3 + NaCl
AgCl + NaNO3
• Can have combustion reactions
• Are ones in which an element or a compound reacts
rapidly with O gas to liberate heat and light energy,
compounds combining with O in these reactions are
hydrocarbons, fuels like kerosene and gasoline, complete
combustion yields CO2 and H2O, if not have enough O
combustion will not be complete – CO and C may be
released
• CH4 + 2O2
light
CO2 + 2H2O + heat +
Lab 5 Will It React?
Question: How can you identify a chemical reaction?
Hypothesis:
Materials: well plate HCl magnesium silver nitrate baking soda
sodium hydroxide copperII sulfate mossy zinc distilled water
pipettes paper towels laminated template goggles aprons
Safety: Goggles must be worn at all times. Do NOT eat or drink
anything during this lab. Wash your hands well before
leaving class.
Procedure:
1. Notice the laminated reaction template taped to your lab
table. This is where you will complete all chemical
reactions.
2. Using the prepared and labeled pipet, add 2- 4 drops of HCl
in the boxes identified on the template. Return the pipet to
the holder. Make observations in Data Table 1.
Lab 5 continued
3.Place another 2-4 drops of HCl on the X in each box indicated where HCl is a
reactant.
4. Repeat with 2-4 drops of copperII sulfate (CuSO4) in the box indicated on the
template.
5. For each row that has a second reactant, add that reactant to the second column.
Write your observations in Data Table 1.
6. Beginning with the first reaction, add the two reactants to the column marked
“product” and observe what happens. Do only one reaction at a time, so you do
not miss seeing any reaction that takes place. Record your observations in Data
Table 1.
7. Continue combining reactants as indicated in the product column and write your
observations for each set of chemicals.
8. When you have completed all combinations wipe the laminated template with a
dry paper towel and through the paper towel in the trash can.
9. After you have cleaned the template and straightened the table be sure to wash
your hands.
Data Table 1
Chemical (s)
HCl solution
HCl + NaHCO3
HCl + AgNO3
HCl + Zn
HCl + Al
HCl + Mg
CuSO4 + NaOH
Observations
Lab 5 cont.
Results:
Conclusion:
1.
Compare and contrast the reactions of Al, Mg, and Zn with
HCl.
2.
Which reaction formed a precipitate?
3.
Which reactions resulted in gas production?
4.
Which reaction resulted in a color change?
5.
Which reaction had no observable change?
6.
What could you do to try to find out if any of these reactions
resulted in a temperature change?
7.
What differences did you see between HCl and CuSO4?
Lab 6 An Exothermic Reaction ?
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Question: How can you tell that a chemical reaction
is exothermic?
Hypothesis:
Materials: test tube test tube holder stirring rod
bleach
goggles
thermometer
hydrogen peroxide eye-dropper shredded steel wool
Procedures:
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1. Goggles and aprons are required for the lab.
2. Get a clump of steel wool about the size of a marble and
shred it.
3. Put the steel wool into the test tube. There should be
about 2cm of steel wool in the bottom of the test tube.
Lab 6 An Exothermic Reaction ? Cont.
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4. While using the clamp to hold the test tube, use the stirring rod to
push the steel wool to the bottom of the test tube. Do not pack it, but
make sure the wool is at the bottom.
5. Pour enough hydrogen peroxide into the test tube so the steel wool
is barely covered.
6. Place the thermometer in the test tube. Make sure the bulb of the
thermometer is in the hydrogen peroxide. After allowing the
thermometer to adjust to the temp. record the starting temperature in
Data Table 1.
7. Once you have recorded the starting temperature add several drops
of the bleach. As the chemical reaction is taking place record the
temperature and record in Data Table 1.
8. Once the reaction has stopped record the final temperature in Data
Table 1.
Clean up the lab table. Pour out your mixture in the bucket in the front
of the room and then rinse out the test tube for the next class.
Data Table 1
Beginning Temp,
Temp. During the
Reaction
Ending Temp.
Lab. 6 Continued
Results:
Conclusion:
1.
Graph your results. Does the graph show this to be an exothermic or
endothermic reaction?
2.
What did you observe when you covered the steel wool with the
hydrogen peroxide?
3.
What did you observe when the drops of bleach was added to the
steel wool and the hydrogen peroxide?
4.
What happened after several drops of bleach was added to the steel
wool?
5.
Did the temp. change? How much did it change? Did it go up or
down?
6.
Based on the graph and your observations is this an exothermic or
endothermic reaction? How do you know?
• activation energy – minimum amt. of
energy needed to start a chemical
reaction
• concentration – amt. of one material in a
given amt. of another material
• catalyst – material that increases the
rate of a reaction by lowering the
activation energy
• enzyme – a biological catalyst
• inhibitor – material used to decrease rate
of a reaction