Gas Laws
Posted: May 28th, 2011, 8:15 pmGas Pressures
Air is a mixture of several gases and the gaseous molecules are in constant motion. This constant motion causes them to collide with objects and exert a pressure. This pressure is known as atmospheric pressure.
As the particles of gas decrease, the collisions are not as frequent, and pressure decreases.
Pressure is the measure of force per unit area.
- SI unit for pressure is the kPa.
- Two other units are still commonly used:
- millimeters of mercury
- atmospheres
Laws
Boyle's Law
At constant temperature and number of moles, the pressure and volume of a gas are INVERSELY related. In other words, as pressure is reduced, the volume increases. And vice versa - if pressure is increased, volume decreases.
Charles' Law
At constant pressure and number of moles, the temperature (in Kelvin --> K = Celsius + 273) and volume of a gas are DIRECTLY related. In other words, if temperature is increased, so will the volume. If it decreases, so does the volume.
Combined Gas Laws
Ideal Gas Equation
An ideal gas is one in which the molecules have no volume and exert no attraction for one another. No ideal gases exist, but under certain conditions of temperature and pressure, real gases approach ideal behavior.
The four variables used to describe the state of a gas can be combined into a single expression.
where R is a proportionality constant known as the ideal gas constant.