Problem 1
Frequently during the semester we will be using atmospheric density, [M], in molecules per cubic centimeter (generally written as molecules cm^-3). 

Starting from the ideal gas law, P = (n/V) RT, derive an equation (or expression) for [M] in terms of P in millibar (mbar), T in Kelvin (K), and a constant.
(That is, [M] = some function of P,T, and a constant).

The gas constant, R, is 0.08206 L atm K^-1 mol^-1 . Note that the quantity [M] is a number density, whereas r is reserved for mass density.

Hint - Note that n/V will be equal to [M] once you convert R into units of (cm³ mbar K^-1 molecule^-1).

Important conversions

1 atm = 1013 mbar
1 L = 1000 cm³
1 mole = 6 x 10²³ molecules