| Videos of combustion experiments and questions for students about the experiments are available.
There are three QuickTime movies that go
with this article. You will need to have
QuickTime 3 or higher installed to view the
movies. A free copy of QuickTime is available
from Apple at http://www.apple.com/quicktime.
Data for the Three Movies:
|
Volume of jar:
Atmospheric Pressure:
Temperature:
Initial Mass of Paper:
Final Mass of Paper:
Initial Pressure:
Maximum Pressure:
Final Pressure:
|
1950 mL
750 torr
23 oC
0.45 g
0.16 g
12 psi (arbitrary set point for ambient)
25 psi (13 psi above ambient)
12 psi
|
Leading Questions for the Three Movies:
For the movie "V.MOV"
(Constant Volume)
The movie size is 773 KB. |
|
1. What amount, in mol, of oxygen exists
in the jar before the reaction?
2. Write a chemical equation for the reaction,
and calculate the amount, in mol, of oxygen
that exists in the jar after the reaction.
3. Explain why the pressure rises rapidly,
then falls rapidly to a point, but falls
slowly thereafter.
4. What would the average temperature for
this mixture of gases need to be to account
for the maximum pressure?
5. Why is the final pressure the same as
the initial pressure?
For the movie "P.MOV"
(Constant Pressure)
The movie size is 293 KB. |
|
Assume that the jar contains about 0.017 mol
of oxygen and about 0.29 g of paper burns.
Estimate the maximum increase in volume. The
jar is a 2 quart canning jar. How do you explain
this change in volume?
Write a chemical equation for the reaction and calculate the masses or volume
of products at various estimated temperatures to substantiate your answer.
Why does the volume decrease rapidly to a small fraction of the maximum,then
decrease very gradually to zero? Why is the final volume change zero?
For the movie "L.MOV"
(Loose Lid)
The movie size is 163 KB. |
|
Here the lid is placed loosely on the jar. Note that there is little evidence
of air escaping. Comparing this experiment to the others, comment on the effect
of confinement in causing reactions to be explosive. Why does the flame go out,
even though air is free to come and go?
|
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