How this calculator works
The universal molar gas constant is common to every gas. Dividing it by molar mass converts the equation of state to a per-kilogram basis. For an ideal gas, the difference between constant-pressure and constant-volume specific heats equals the same mass-specific constant. The heat capacities must refer to the same composition, state and mass basis; mixing molar and mass-specific data gives the wrong units.
Formula
Rs = R/M; Rs = cp - cv; cp = cv + Rs; cv = cp - Rs.
Worked example
A gas with M = 0.02 kg/mol has Rs = 415.7231309 J/(kg K). Heat capacities cp = 1005 and cv = 718 J/(kg K) give Rs = 287 J/(kg K).
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Frequently asked questions
Can I use g/mol?
Divide by 1000 before entering the molar-mass field.
Why must cp exceed cv?
For an ideal gas, additional constant-pressure heating supplies expansion work, so cp - cv equals a positive gas constant.
Is R adjustable?
This page uses the exact SI value 8.31446261815324 J/(mol K), derived from defining constants.