Charles Law Lab
H2O Vapor

Gas Laws Notes


Room conditions: 640 mm Hg and 22C unless otherwise specified.
(Use the actual barometer reading on lab days!)

STP: 760 mm Hg and 0C
1 Torr = 1 mm Hg pressure
1 Atm = 760 mm Hg
1 Atm = 1013.25 mbar

To convert our barometer in mbar to mmHg use factor-label method.

854 mbar 760 mm Hg
  1013.25 mbar

=  640.55 mm Hg. (air pressure does change with weather systems)

To convert mmHg to mbar use factor-label again. Cool Huh!!!!?

684 mmHg 1013.25 mbar
  760 mm Hg

= 911.93 mbar

K = C + 273

Always use K in gas problems.
degrees A are the same as degrees K

When working on gas laws, don't forget to use your common sense. You probably already know what will happen at the new conditions. Think of the balloon in a hot car going over the Sierra's

Boyle's Law: If you double the pressure, you will halve the volume.

Charles' Law: If you double the temperature you will double the volume.

Combined Gas Law: Depends on whether you got it hotter, or increased the pressure more? Both temperature and pressure can vary.

Ideal gas law: most gases are "nearly ideal". This works well over "small" temperature or pressure ranges for nearly all gases. The volume and pressure depend on the amount of gas and its temperature. You need R the gas constant (fudge factor) to make everything come out right. 

R = 0.0821 (L atm )/( K mole)

Use atm of pressure.
Liters of volume
Kelvins of temperature
Moles  of mass

The gas constant has a compound unit so that 3 of the 4 units will cancel (if your set-up is right) and you'll magically be left with the correct units! Spiffy.