To completely describe the state of a gaseous substance, its pressure, volume, amount, and temperature
must be specified.

PRESSURE
    Pressure is defined as force per unit area. The SI unit of pressure is the pascal (Pa), the pressure
    exerted by a force of one newton on an area of one square meter.  Atmospheric pressure is about
    10⁵ Pa or 100 kilopascals (kPa).   The pressure units used most frequently are atmosphere (atm)
    or millimeters of mercury (mmHg).   The unit mmHg is often called the Torr.

           1 atm = 760 mmHg = 760 Torr

VOLUME
    A gas expands uniformly to fill any container in which it is placed. This means that the volume of a
    gas is the volume of its container. Volumes of gases are often expressed in liters or cubic decimeters.

            1 L = 1 dm³

AMOUNT
    Most commonly, the amount of matter in a gaseous sample is expressed in terms of the number of
    moles (n).   In some cases, the mass is given instead. These two quantities are related through the
    molar mass, MW.

            n = mass/MW

TEMPERATURE
    The temperature of a gas is ordinarily measured using a thermometer marked in degrees Celsius.
    However, in any calculation involving the physical behavior of gases, temperatures must be
    expressed on the Kelvin scale (K).  The formula for converting between ^oC and K is:

                K = ^oC + 273.15

    The conditions of 0^oC (273.15 K), and 1 atm (760 Torr, 760 mm Hg) are referred to as standard
    temperature and pressure (STP).

IDEAL GAS LAW
    The pressure, volume, amount, and temperature of a gas are described mathematically by an
    equation known as the ideal gas equation.

     PV = nRT

    The gas constant, R has a given value depending on the unit of pressure.
                    R = 0.0821 L^.atm/mol^.K   (pressure is in atm)
                       =  62.4 L^.mmHg/mol^.K  (pressure in mmHg)
                       =  62.4 L^.Torr/mol^.K     (pressure in Torr)

EXAMPLE 1
Calculate the volume occupied by 93.6 grams of NO gas at a pressure of 793 mmHg at 100 ^oC.
[Answer:  91.6 L]
 
 
 
 
 
 
 

EXAMPLE 2
Calculate the mass of ammonia, NH₃, in a 6.64 L cylinder if the pressure inside the cylinder is
4.76 atm at 25.0 ^oC.
[Answer: 22.0 g NH₃]
 
 
 
 
 
 
 

EXAMPLE 3
What is the pressure (mmHg) inside a 10.0 L vessel containing 8.025 g CH₄ at 20.0^oC?
[Answer: 914.6 mmHg]
 
 
 
 
 
 
 

EXAMPLE 4
When a 0.308 g sample of liquid hexane, C₆H₁₄, was vaporized at 100.00^o C, the pressure of the
hexane vapor at this temperature was 759.42 mmHg.  The volume of the vapor was 112.40 mL.
Using this set of data, calculate an experimental molar mass for hexane.
[Answer:  84.02 g/mol]