Gas Behavior & Gas Laws
One state of matter deserves extra-special attention: Gas.
Gases are incredibly important to our daily lives - they allow us to (among many other things) play sports, travel, cook, and (incredibly important to life) breathe!
They are also unique; gases behave differently than solids or liquids, and have a different structure at the atomic level, even though they are made of the same substances. In general, gas particles have a large amount of space between them, and the volume of a gas can change because of temperature and pressure.
This variability in volume and reaction to temperature change causes gases to behave in unique ways.
Temperature & Gas
Temperature is simply a measure of how fast the particles in an object are moving.
The faster they move, the more energy they have, and the higher the temperature is.
Gas Pressure
The amount of force exerted on a given area of surface.
In a gas, this is relative to the number of times the particles of a gas hit the inside of their container.
So, if you add more gas to the inside of an object – say, filling up a basketball – you end up with a harder object. There is more pressure inside the ball because there are more gas particles striking the inside of the container (the ball).
Gas Behavior Laws
Luckily for us, as scientists, there are laws that describe the behavior of gas in relationship to temperature and pressure.
Boyle’s Law
Penned by physicist Robert Boyle in 1662, it states that:
for a fixed amount of gas, at a constant temperature, the volume of gas is inversely related to the pressure.
This law gives the relationship between pressure and volume if temperature and amount are held constant: If the volume of a container is increased, the pressure decreases; if the volume of a container is decreased, the pressure increases.
Why?
Suppose the volume is increased. This means gas molecules have farther to go and they will impact the container walls less often per unit time. This means the gas pressure will be less because there are less molecule impacts per unit time.
If the volume is decreased, the gas molecules have a shorter distance to go, thus striking the walls more often per unit time. This results in pressure being increased because there are more molecule impacts per unit time.
The mathematical form of Boyle’s Law is: PV = k
This means that the pressure-volume product will always be the same value if the temperature and amount remain constant. This relationship was what Boyle discovered.
This is an inverse mathematical relationship. As one quantity goes up in the value, the other goes down.
In the animation above, notice the data table to the right - as you decrease the overall volume of the gas in the syringe, the recorded pressure increase directly. As noted above, it is an inverse relationship.
Another important law regarding gases is Charles’ Law.
First published by Joseph Louis Gay-Lussac in 1802, it states the following:
For a fixed amount of gas at a constant pressure, the volume of the gas changes in the same way as the temperature of the gas.
In other words, if the temperature of a gas increases, the volume of the gas will increase by the same amount.
This is a fairly simple concept, and in fact, may be rationalized using simple logic.
Suppose we have a container of gas that we heat. As the heat of a gas increases, so does the relative energy of the particles of gas. These particles begin to move more quickly and make contact with the walls of their container more often, thereby increasing the pressure. Simple!
In the animation above, as you drag the temperature slider to the right and increase the temperature of the gas, the pressure in the chamber increases. This is indicated by the rising lid on the chamber.
Posted in Matter & Properties of Matter, Physics & Physical Science
