The deviation of nitrogen from Boyle's law at various temperatures is seen from the subjoined table. Under relatively low pressures the molecular-attraction effect causes the gas to be more compressible, with the result that the product pv decreases in value. As is the case with most other gases, however, the molecular volume effect soon shows its influence, and the value of pv increases with the pressure; the gas is less compressible on account of the fact that the molecules now occupy an appreciable fraction of the total volume.
The graphical relationship between p and pv shows how, at 0° C., the latter diminishes at first with rise of pressure, and, after reaching a minimum, increases again throughout with rise of pressure. As is usual, the isotherms at higher temperatures show a progressive shift of the minimum towards the region of lower pressures, and finally the minimum disappears.
The limiting value of pv for nitrogen at zero pressure and 0° C., and the molecular weight from the ideal densities under these conditions, may be calculated as follows: -
The value of pv for nitrogen increases with decrease of pressure from 1 atmosphere to zero, which also occurs with most other gases, with the exception of hydrogen.
The coefficient α= =-0.00056 for nitrogen.
The corresponding value for oxygen is -0.00094, and by using Rayleigh's values for the densities under normal conditions, the molecular weight of nitrogen is given by =28.016, where 32=molecular weight of oxygen.
The corresponding value calculated by D. Berthelot from the results of Leduc and Sacerdote is 28.013.Relation between pressure and volume of nitrogen | Pressure in Atm. | pv at 0° C. | pv at 16.03° C. | pv at 99.45° C. | pv at 199.5° C. | | 1 | 1.0000 | - | - | - | | 100 | 0.9910 | 1.0620 | - | - | | 200 | 1.0390 | 1.1145 | 1.4890 | 1.9065 | | 300 | 1.1360 | 1.2105 | 1.5905 | 2.0145 | | 400 | 1.2570 | 1.3290 | 1.7060 | 2.1325 | | 500 | 1.3900 | 1.4590 | 1.8275 | 2.2570 | | 600 | 1.5260 | 1.5945 | 1.9545 | 2.3840 | | 700 | 1.6615 | 1.7290 | 2.0865 | 2.5125 | | 800 | 1.7980 | 1.8655 | 2.2200 | 2.6400 | | 900 | 1.9340 | 2.0015 | 2.3540 | 2.7715 | | 1000 | 2.0685 | 2.1360 | - | - | | 1500 | 2.7202 | - | - | - | | 2000 | 3.3270 | 3.3980 | - | - | | 2500 | 3.9200 | - | - | - | | 3000 | 4.4970 | 4.5675 | - | - | |