For example, compressing 1 kg of nitrogen from 1 bar to 200 bar costs at least : ( h c − h a ) − T a ( s c − s a ) . With the data, obtained with the T – s diagram, we find a value of (430 − 461) − 300 × (5.16 − 6.85) = 476 ⁠ kJ / kg ⁠ .