Chapter 14 Laboratory: Gas Chemistry 247EvdRE y Ay GAS CHEmISTRy
The importance of gas laws isn’t limited to chemistry labs. Applied gas laws are important in everyday life, including at least one
application that we literally couldn’t live without. Here are just a few of them:- Every breath you take illustrates Boyle’s Law. When you inhale, your muscles expand the volume of your chest and lungs,
reducing the gas pressure inside. Outside air, at constant atmospheric pressure, enters your lungs until the pressure
equalizes. When you exhale, the volume of your chest and lungs decreases, increasing the gas pressure above ambient
atmospheric pressure. Air exits your lungs until the pressure equalizes. - Diesel engines use the physical manifestations of gas laws to produce power. During the intake stroke, the engine
cylinder fills with a mixture of air and vaporized diesel fuel at relatively low pressure. During the compression stroke,
the piston compresses the fuel-air mixture to a volume that’s only a few percent of its original volume, which increases
the temperature (Charles’ Law) sufficiently to ignite the fuel-air mixture without a spark. Because one molecule of
hydrocarbon fuel reacts with oxygen to form many molecules of carbon dioxide and water vapor, the total number of
moles of gas increases (Avogadro’s Principle). The combustion of the fuel-air mixture produces a great deal of heat, which
increases pressure in the cylinder (Gay-Lussac’s Law). Because the piston is free to move within the cylinder, the increased
pressure forces it outward, producing power. That power is transferred via the drive train to the wheels, moving the vehicle. - Refrigerators and air conditioners are closed systems that use the physical manifestations of gas law to transfer heat. The
compressor compresses a gas (sometimes so far that the gas becomes a liquid), during which the temperature of the gas
increases according to Charles’ Law. The compressed gas is passed through a heat exchanger, where it gives up most of
its heat to the outside environment. The cool compressed gas is then passed through cooling coils, where it is permitted
to expand, reducing its pressure and (again according to Charles’ Law) its temperature by the Joule-Thompson effect.
The cold gas absorbs heat from the outside environment, cooling it. The cycle is then repeated, resulting in a net transfer
of heat from one place (such as the inside of the refrigerator or the inside of your home) to another place (such as the
outside of the refrigerator or your home). The same process is used in reverse by heat pumps, which transfer heat from
the cold outside air to the warmer air inside your home. - Automobile air bags illustrate Avogadro’s Principle dramatically (and loudly). An air bag is simply a large balloon
constructed of very strong material and with all gas exhausted from it. The air bag mechanism includes a small canister
that contains 50 g to 200 g of solid sodium azide (NaN 3 ) or a similar propellant. When the air bag deploys, the sodium
azide reacts almost instantly to form metallic sodium and nitrogen gas. In about 50 milliseconds (0.05 second), the
airbag that originally contained almost no gas is filled with sufficient nitrogen gas to inflate it completely. (Sodium azide is
extremely toxic, more so than potassium cyanide, so don’t mess with it at home.)
SI SySTEm
SI = International System of Units from the French, Le
Système International d’Unités. SI is the modern form of
the now-obsolete metric system. Some metric system
units (e.g. centimetre, litre) are deprecated in SI and
replaced with the SI standard units (metre and cubic
decimetre, respectively).