## Extra Credit 2

### Gas Properties

In this exercise you will investigate some thermometric properties of gases.
The ideal gas law states that for a fixed volume of an ideal gas (PV/T) = nR = constant.  Here P and V are the pressure and volume of the gas at absolute temperature T.  Theoretical derivations of the ideal gas law neglect the forces that the gas molecules exert on each other.  Real gases therefore do not strictly obey the ideal gas law.  However, at sufficiently low densities, intermolecular forces do not play a significant role and the ideal gas law becomes increasingly accurate.  For instance, at 20 atm pressure and room temperature, the volume of 1 mole of oxygen gas is about 2.3% smaller than predicted by the ideal gas law, but at 1 atm pressure the volume is only about 0.13% smaller.

• If the temperature T is constant the ideal gas law yields Boyle's law, PV = constant (at constant T).
• If the pressure is held constant, the ideal gas law yields Charles's law, V/T = constant (at constant P).

Procedure:

Open a Microsoft Word document to keep a log of your experimental procedures and results.  Complete all the tasks (in blue).  Answer all questions.

Use an on-line simulation from the University of Colorado PhET group to verify Boyle's law and Charles' law.

(a)  Explore the interface!  (Click "Help" for hints.)

• You can pump two types of molecules into the chamber.
• You can specify constant volume, pressure, or temperature.
• You can work in an environment with or without gravity.
• You can heat up the gas in the chamber.
• You can use various measuring tools. (Explore what they can be used for.)

(b)  Reset the simulation, choose constant volume and a gravity-free environment and add gas to the chamber at 300 K until the pressure is between 1 and 2 atm.
Switch to constant temperature and verify Boyle's law.  Boyle's law states  that PV = constant for constant T, or P = constant/V.
A plot of P versus 1/V should yield a straight line.  If it does, you have verified Boyle's Law.

[The volume of the box is V = length * width * height.  Width and height are fixed, so  V = constant*length.  Let us set the constant to 100 nm2.  The length can be measured with the ruler in units of nanometer (nm).]

(c)  Switch to constant pressure and verify Charles' law.  Charles' law states V = constant * T for constant P, where T is the absolute temperature.  A plot of V versus T should yield a straight line.  If it does, you have verified Charles' Law.