thermodynamics

Question

How do you find the specific volume with just temperature and pressure given?

Answer 1

This can be done for an idea gas if you know the molar mass of the gas.

 

The starting point is the ideal gas equation PV =  n RT.     Divide both side by P and n to get

 

   V/n  =   R T/ P

 

V/n is a type of specific volume, namely the molar volume.     If T =  273K and P = 1 atm,  it

is  22.4 L.

 

To get a mass based specific volume, divide   V/n  by the Molar mass  (M).   The molar mass is the mass of one gram.  For example,   for neon   M =  20.18 g

 

In symbols ,  the specific volume is     R T/ (P M)

 

This can be worked out to a number if you know  P, T and M.

 

It should be noted that for any real gas (neon for example), this is an approximation.    It is very good for the noble gases but very bad for gases such as propane which are far from ideal.