Kinetic Theory of Gases - Chemistry LibreTexts
The module presents the ideal gas equation and explains when this Because they both equal the same constant, the gas's pressure and volume under two. Navigating the world of chemistry is much easier once you've got an A compound is composed of two or more elements chemically combined in a defined ratio by weight. The state of an ideal gas is determined by its pressure, volume, and. Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology. The relationship of a gas with pressure and volume was developed by the.
Be advised that this particular example is one in which the assumption of ideal gas behavior is not very reasonable, since it involves gases at relatively high pressures and low temperatures.
Scuba divers, whether at the Great Barrier Reef or in the Caribbean, must be aware of buoyancy, pressure equalization, and the amount of time they spend underwater, to avoid the risks associated with pressurized gases in the body. Pressure increases with ocean depth, and the pressure changes most rapidly as divers reach the surface.
The pressure a diver experiences is the sum of all pressures above the diver from the water and the air. Every 33 feet of salt water represents 1 ATA of pressure in addition to 1 ATA of pressure from the atmosphere at sea level. Divers must therefore undergo equalization by adding air to body airspaces on the descent by breathing normally and adding air to the mask by breathing out of the nose or adding air to the ears and sinuses by equalization techniques; the corollary is also true on ascent, divers must release air from the body to maintain equalization.
Buoyancy, or the ability to control whether a diver sinks or floats, is controlled by the buoyancy compensator BCD. The expanding air increases the buoyancy of the diver, and she or he begins to ascend. The diver must vent air from the BCD or risk an uncontrolled ascent that could rupture the lungs.
In descending, the increased pressure causes the air in the BCD to compress and the diver sinks much more quickly; the diver must add air to the BCD or risk an uncontrolled descent, facing much higher pressures near the ocean floor.
Boyle's law - Wikipedia
The pressure also impacts how long a diver can stay underwater before ascending. The deeper a diver dives, the more compressed the air that is breathed because of increased pressure: If a diver dives 33 feet, the pressure is 2 ATA and the air would be compressed to one-half of its original volume.
The diver uses up available air twice as fast as at the surface. Standard Conditions of Temperature and Pressure We have seen that the volume of a given quantity of gas and the number of molecules moles in a given volume of gas vary with changes in pressure and temperature. Even on a molecular level, air and helium are different: Air is a mixture of nitrogen, oxygen, and other gases, while helium is a single gas. But helium and air have many things in common with each other, and even with substances like deadly carbon monoxide and flammable hydrogen.
At standard temperature and pressure, these substances are all gases, one of the common states of matter see our module States of Matter for more information. All gases share common physical properties. Like liquidsgases freely flow to fill the container they are in. But while liquids have a defined volumegases have neither a defined volume nor shape. And unlike liquids and solidsgases are highly compressible. These common properties relate to a unique characteristic of gases: Gas molecules are incredibly far apart and rarely interact with each other.
In solidsthe attractive and repulsive forces between molecules—the intermolecular forces—are so strong they lock the solid into a fixed shape and size, as discussed in our Properties of Solids module. In liquidsthe intermolecular forces are weaker, and liquid molecules can move around each other. But a liquid's molecules are still close enough that intermolecular forces affect nearby molecules see our Properties of Liquids module. The different types of liquids and solids such as molecular and network solids have properties that reflect the unique ways their molecules interact.
As a result, all gases share some common behaviors. Early scientists explored the relationships among the pressure of a gas P and its temperature Tvolume Vand amount n by holding two of the four variables constant amount and temperature, for examplevarying a third such as pressureand measuring the effect of the change on the fourth in this case, volume.Boyle's Law
The history of their discoveries provides several excellent examples of the scientific method. The Relationship between Pressure and Volume: Boyle's Law As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced closer together.
Conversely, as the pressure on a gas decreases, the gas volume increases because the gas particles can now move farther apart. Weather balloons get larger as they rise through the atmosphere to regions of lower pressure because the volume of the gas has increased; that is, the atmospheric gas exerts less pressure on the surface of the balloon, so the interior gas expands until the internal and external pressures are equal.
The Irish chemist Robert Boyle — carried out some of the earliest experiments that determined the quantitative relationship between the pressure and the volume of a gas.
Boyle used a J-shaped tube partially filled with mercury, as shown in Figure 6. In these experiments, a small amount of a gas or air is trapped above the mercury column, and its volume is measured at atmospheric pressure and constant temperature.
More mercury is then poured into the open arm to increase the pressure on the gas sample.
Kinetic Theory of Gases
The pressure on the gas is atmospheric pressure plus the difference in the heights of the mercury columns, and the resulting volume is measured. This process is repeated until either there is no more room in the open arm or the volume of the gas is too small to be measured accurately.
This relationship between the two quantities is described as follows: Dividing both sides of Equation 6.