A group of novice backpackers begin their
trek through Alaska’s frontier in mid-February, as the sun shines down in a
false display of warmth. But soon, as the sun goes down, even this little
warmth flees for the night, and the backpackers find themselves shivering
around a small fire in the subzero, freezing weather. Frigidly preparing what
might be called a meal, the backpackers realize, much to their dismay, that
while they’re surrounded by cans of beans, they can’t open a single one of them
since the one-and-only can-opener that they brought along for the trip has
disappeared. Sitting around the fire, mulling over their own stupidity of only
bringing one can-opener and then having lost it, one of the backpackers, Joe,
comes up with a brilliant idea. “Why not throw the cans into the fire?” Joe
says in complete innocence. “The fire’s bound to burn a hole into the cans or
somethin'.” And so, novice as they are, the backpackers begin throwing cans
onto the fire, hoping that the heat will break open the cans to feed their
hungry stomachs.
Just minutes after the labels begin to burn away, revealing the aluminum sides,
a loud explosion bursts through the air from the fire, like the sound of a
bomb, followed by another and another. The backpackers throw themselves to the
ground, just in time before the explosions get really severe. Waiting for
several minutes after the last explosion goes off, Joe and the other
backpackers warily rise, surveying the fire, only to see that the cans have
opened up, for sure, but that no beans remain in the bulged, twisted,
corpse-like cans. Looking around, their entire campsite stands in relative
order, except for the thin layer of beans splattered everywhere. Tents,
backpacks, and hiking gear, all covered with a mucilaginous film of delicious,
“premium quality” beans, lie quite dilapidated. In shock, the backpackers pull
their sleeping backs out of their tents to sleep beside the fire, not having
the energy to clean up the mess or to try some different strategy for getting
food.
You’re probably thinking right about now, “How on earth does this tie into
chemistry?” or maybe even “What a bunch of dumb campers!” The truth of the
matter is, while those backpackers sure didn’t seem to have a lot of sense in
them, they did at least have a tenative grasp of one, crucial principle that we
are learning in chemistry these days. And that is that as you increase the
temperature (T) of a gas, its pressure (P) increases as well.
Mathematically, we could show this relationship as follows: P/T = constant. So,
if that gas is contained in a sealed vessel--such as a bean can--then by
increasing the temperature enough and, by consequence, the pressure, the
container should, in theory, explode. The only problem, obviously, is that the
cans don’t explode kindly as we might want them to, emitting a little “beep”
when they’re done like a good and proper microwave would. No, instead, as the
thin layer of air that was trapped at the top of the cans of beans expanded
with the increasing heat from the fire, the pressure increased as well, pushing
a tremendous force against the sides of the cans until they eventually gave way
and threw the beans along with the air in a disgusting slurry all around the
campsite.
This is but one practical application of what we’ve been studying right now in
chemistry class. The above direct relationship between pressure and temperature
(P/T = constant) is referred to as Gay-Lussac’s Law because it was discovered
by a French scientist named Joseph Louis Gay-Lussac. Many other relationships
between the volume, pressure, and temperature of a gas have been discovered,
but this is one of the crucial laws that was used to create what is called the
Combined Gas Law, which is slightly more complex, and so will not be explained
here.
Chemistry is oftentimes made abstract and separate from everyday experiences,
which is a terrible shame since it is based upon the experiences of scientists
who observe what goes on in the natural world. And so, to both tie chemistry
into everyday life and to illustrate the power of using Gay-Lussac’s Law on its
own in a real-life scenario, consider for a moment the pressure in your bicycle
tires. Your friend Joe--who luckily survived the little incident in Alaska--reads his bicycle manual amazingly, and it tells him that his bicycle tires
should have a pressure of nearly 70 pounds per square inch (PSI). So, as Joe
plans on heading off soon for a cross-country biking trip in the hot and humid
state of Arizona, he checks his bicycle for any signs of damage, pumps the
tires up to the correct pressure, and heads off from his northerly home in
Maine to southern Arizona to meet up with some friends of his. Getting out of
his taxi car from the drive from the airport to his friend’s house, Joe and his
friends get their stuff together and head off to bike for the day. The sun is
shining, with not a cloud to be seen in the sky, and Joe’s friends warn him to
wear sunscreen and to bring plenty of water because the temperature is supposed
to peak in the lower 100s (Fahrenheit).
As Joe rides his bike along on the trip, enjoying the scenic view of Arizona,
he get the uneasy feeling that something’s not quite right. His tires seem like
their standing up on edge, and he feels like he’s riding along on a tight-rope.
Thinking it his imagination, he continues riding, but after not even ten more
minutes, his front tire bursts, and Joe and his friends have to go back to the
house to get a new one, his bicycling trip spoiled for the day.
What could have prevented this accident is a proper knowledge of the fact that
as temperature of the air inside the tires of the bike increase, so does the
pressure of the air. Joe pumped up his bicycle’s tires to the correct pressure,
while standing in the cool, 70 degree garage, way up in northern Maine, but
when he brought his bicycle down to Arizona, the temperature was far from 70
degrees Fahrenheit, and so the pressure and volume of the tires increased as
well, so much that it actually blew one of them.
Like Boy Scouts should, be prepared for anything, and take with
you--along with more than one can-opener and several extra tires for your bike
on any trip you make--the knowledge that the temperature and pressure of a gas
are both interconnected, and that as you change one, you will most likely
change the other. This change will either to your delight as in making
popcorn or to your dismay, like Joe, our friend, who deserves a medal of honor
for all he's been through in this report.
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