Robert Boyle.

Boyle's Law, named after physicist Robert Boyle

It makes sense if you think about it. The pressure that the gas exerts on the walls of the container is caused by gas particles colliding with the wall. If we make the container that we're holding the gas in bigger (by increasing the volume) the gas particles have more room to do their thing without hitting the walls as often, which decreases the pressure. Or if we make the container smaller the gas particles will run into the walls more often, thereby increasing the pressure.

On paper, Boyle's law takes the form:

PV

where

A typical plot of pressure versus volume for a gaseous sample can be found here. At any point on the curved line

This equation will be most useful when solving questions regarding Boyle's law.

P

V

T

P

V

T

P

V

Joseph Louis Gay-Lussac.

That fancy guy above is Joseph Louis Gay-Lussac, a French chemist and physicist who developed Charles' law, the relationship between temperature and volume in gases. Confused why it's called Charles' law and not Gay-Lussac's law? Gay-Lussac was an honest guy and he gave rightful credit to the unpublished work of Jacques Charles.

Let's think about this. When we increase the temperature of a gas we are increasing the kinetic energy of the particles and making them more excitable. They are moving faster and jumping around a lot more. The gas particles are also colliding with the container walls more often and with more force. As a consequence, the pressure of the gas inside the container increases. Wait a minute. Didn't we just say Charles' law declares pressure and molar volume are held constant? We did. The greater pressure in turn pushes the container walls outward, increasing the container's volume. Overall the pressure does not change, it remains constant and all is right in the world of chemistry. Check out this neat NASA animation of Charles' law in action.

Charles' law is written as:

where

Above is a typical graph of volume versus temperature for gases. At any point on the line

Remember to convert any temperature given in Celsius to Kelvin before solving a problem with Charles' law.

There are a lot of videos that show Charles' law in action. Watch this hot air balloon inflate. As the temperature of the gas inside the balloon is heated with a flame the balloon begins to inflate because the volume is increasing. Or check out this implosion of a metal drum. The drum is filled with a gas. When the gas is cooled the volume decreases and destroys the drum.

P

V

T

P

(note the pressure is held constant)

V

T

V

Avogadro's law is simple. It states: equal volumes of gases at the same pressure and temperature contain equal number of particles. Mathematically it is expressed:

where

Much as the name implies the combined gas law is a combination of Boyle's law and Charles' law. It states that, for an ideal gas undergoing change from one state (with

where

P

V

T

Emil Clapeyron.

That fine gentleman reading the daily newspaper is Emil Clapeyron.

The only variable we haven't discussed is

P = 900 mm Hg

T = 27°C + 273 = 300 K

V = 15.0 L

R = 0.0821 L•atm/mol•K

PV = nRT

This gas law is pretty straightforward. If we have a mixture of gases in a container, according to Dalton's law, the total pressure is the sum of the pressures exerted by each of the gases in the mixture. Here's the equation that just might change your life:

P

where

Thomas Graham.

That Graham guy sure was perceptive. He discovered that the denser a gas is, the more slowly it

Upon comparing the rates of effusion of two gases, Graham also said that the inverse ratio of the square roots of the masses of the two gases' molecules equals their relative rate of effusion. Say what? It makes more sense if you see the equation. Here it is:

where M1 and M2 are the total masses of the gas particles. The total mass of hydrogen for example is 1, while the total mass of oxygen is 16. Still confused? It will all make sense once we do a few exercises.