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Gas laws
GAS LAWS
There are three fundamental gas laws that have been developed to describe the relationship between temperature, pressure, and volume of gas. Before getting into the three gas laws (plus the ideal gas law), you need to know the difference between the ideal gas or “perfect” gas and real gases. The ideal gas has three properties:
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• It has particles that are so small that they do not occupy any space of their own.
• It has a constant, straight line, and random movement of particles.
• Particles only collide elastically with the walls of the container and with each other with no forces between the particles of the gas.
Real gases differ from ideal gases in two specific ways. First, as the pressure increases, the volume does not approach zero because, in fact, the molecules do occupy space and have a certain volume. Second, there are intermolecular forces between gas molecules, particularly at low temperatures when molecular motion slows down. At high temperatures and even at moderate temperatures, the intermolecular forces are considered negligible, however.
Gases do behave more ideally at high temperatures. This is because there is expansion of the gas so the molecular volume (the volume of each molecule) does not play a major role. In addition, the molecules are moving so fast that they do have an elastic behavior when bumping against each other and against the walls of the container they are in. Gases are most non-ideal when they are at cold temperatures, which allow for attractive or repulsive forces to take place between molecules. They also do not behave ideally at high pressures because the volume of the molecules becomes a factor.
The molar volume can be worked out of a gas if you know its density at a particular pressure and temperature. For gases, the density is highly dependent on the temperature and pressure. This means that when referring to the density of gases, we are talking about the density at STP, where STP means standard temperature (0 degrees Celsius) and pressure (o ne atmosphere). Standard gas density is the density of gas at STP. The official IUPAC unit for gas density Is kilograms per meter squared, which is also one gram per liter.
