I was saying a closed volume - where state one is at a temperature, T1, and state two is at a lower temperature, T2. If it is a closed control volume then the initial mass, m1, is equal to the final mass, or m2.

PV=nRT is the same thing as PV=mRT is the same thing as P=pRT.

When using mols R is kj/(kmol*Kelvin), when using mass it is kj/(kg*Kelvin), or perhaps even BTU/(lbmass*Rankine) depending on SI or US units.

Mass=mols*atomic mass in g/mol or kg/kmol.