Applications of Gas Laws
One of the most amazing things about gases is that, despite wide
differences in chemical properties, all the gases more or less obey the gas laws.
The gas laws deal with how gases behave with respect to pressure, volume,
temperature, and amount.
The mathematic equation is equally as simple: PV=K where P=Pressure,
V=Volume and K is simply a constant. This has become a basic principle in
chemistry now called Boyle's law and is included as a special case into the more
general ideal gas law
Robert Boyle (1627-1691). In 1662, Robert
Boyle discovered that when held at a
constant temperature, the volume and
pressure of a gas are inversely
proportionate. Put simply, when the
volume goes up, pressure drops, and vice
Boyle’s Law Examples:
Typically we will take a bottle of soda, slowly turning the cap allowing the
air to gradually escape before completely removing the lid. We do this because
we've learned over time that popping it open too fast causes it to fizz up and
spill all over you and everything around you.
Carbonation is exactly as it sounds. Water is pumped full of carbon
dioxide, causing it to bubble up as the CO2 makes its escape. Throw some syrup
in the mix, and you have soda pop. When a soda bottle is filled, it is also
pressurized. Much like the aerosol can, mentioned earlier, when you slowly open
the cap, the gas is suddenly able to increase its volume in order to decrease the
pressure. Since the soda itself is carbonized, the CO2 gasses decide they want to
escape as well, and you have your fizz.
All is fine and dandy, until you shake the bottle up. Shaking up the bottle
causes that neat pocket of carbon dioxide gas in the top to mix in with the
soda. Now pop the cap off. Suddenly all of these excess gas bubbles within the
soda want to expand and escape their high pressure environment as well.
Rather than being able to expand and shoot out of that neat pocket of air with
a pffffffft, they expand while they're still in the soda. As it tries to muscle its way
out, it pushes the soda along with. Pressure in the bottle goes down, volume of
the gas goes up, and you have yourself a mess to clean up.
While there are a couple different types of aerosol cans, one being a little
more elaborate than the other, they both operate off of the same basic
principle: Boyle's law. We'll examine the more elaborate of the two, since it's far
We know that before you spray a can of paint you are suppose to shake it
up for a while, listening as a ball bearing rattles around inside. There are 2
substances inside the can, one being your product, paint for example, the other
being a gas that can be pressurized so much, that it retains a liquid state even
when it is heated past its boiling point. This liquefied gas will be a substance that
has a boiling point far below room temperature. The can is sealed, preventing
this gas from boiling and turning into a gaseous state. That is, until you push
down the nozzle. The moment the nozzle goes down, and the seal is released,
there is now an escape route. The propellant instantly boils and expands into a
gas and pushes down on the product trying to escape the high pressure, and
expand it's volume the atmosphere where there is less pressure. This forces the
product to shoot out from the nozzle, and you have a coat of paint.
What's interesting is that the person who published it, Joseph Gay-Lussac,
insisted on crediting it to Jacques Charles' unpublished work of 20 years earlier.
Charles' law is seen in action in many everyday examples. Here are some of
Jacques Charles (1746 - 1823). The foundation
of basic physics and chemistry are a few
simple but extremely important laws. Charles'
law states that, keeping everything else
constant, there is a direct relationship between
the volume of a gas and its temperature as
measured in degrees Kelvin. Charles' law was
first published in 1801.
Charles’s Law Examples:
Helium Balloon on a Cold Day
If you have bought a helium balloon for your child, you may have noticed
this phenomenon. If it's cold outside, your child's face may fall when she notices
that the helium balloon has crumpled. All isn't lost, of course, because once you
enter your warm home, the balloon returns to its original shape. This is because,
according to Charles' law, a gas takes up more space when it is warm.
The Dented Ping Pong Ball
If you are into ping-pong, also called table tennis, a dented ping pong
ball is something you have probably encountered. Rather than discard it, you
can restore it by placing it into a saucepan half filled with water. Apply gentle
heat to the saucepan, stirring constantly. If the ball is not cracked by the dent,
the air inside will expand as it heats, pushing out the dent and restoring the ball
to its original shape.
Gay-Lussac's Law states that the pressure of a fixed amount of gas at fixed
volume is directly proportional to its temperature in Kelvin.
Simplified, this means that if you increase the temperature of a gas, the
pressure rises proportionally. Pressure and temperature will both increase or
decrease simultaneously as long as the volume is held constant.
Joseph Gay-Lussac (1778-1850). Gay-
Lussac’s Law is an ideal gas law where at
constant volume, the pressure of an ideal
gas is directly proportional to its absolute
temperature. In other words,
Gay-Lussac’s Law Examples:
Firing a bullet.
When gunpowder burns, it creates a large amount of superheated gas.
The high pressure of the hot gas behind the bullet forces it out of the barrel of
A burning automobile tire.
The heat from the burning rubber will cause the air pressure in the tire to
increase. This can cause the weakened tire wall to explode.
The carbon dioxide forms bubbles, and, as the yeast continues to leaven
the dough, the increase in the number of particles of carbon dioxide increase
the volume of the bubbles, thereby puffing up the dough.
Amedeo Avogadro (1776-1856). Avogadro's
Law, along with other gas laws, explains why
bread and other baked goods rise. Yeast or
other leavening agents in the dough break
down the long carbohydrates from the flour
or sugar and convert them into carbon
dioxide gas and ethanol.
Avogadro's Law Explainations
Projectiles, like cannons and guns; the rapid reaction of the gunpowder
very suddenly creates a large amount of gas particles--mostly carbon dioxide
and nitrogen gases--which increase the volume of the space behind the
cannon or bullet until the projectile has enough speed to leave the barrel.
A balloon inflates because of Avogadro's Law; the person blowing into
the balloon is inputing a lot of gas particles, so the balloon increases in volume.
We breathe because of Avogadro's Law, among others; the lungs expand, so
more gas particles can enter the lungs from the outside air (inhaling). Then the
lungs contract, so the waste gas particles are expelled (exhaling).
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