259 

 TABLES 241-253.— TEMPERATURE, PRESSURE, VOLUME, AND 

 WEIGHT RELATIONS OF GASES AND VAPORS 



TABLE 241.— SIMPLE GAS LAWS 



Any amount of gas completely fills the space in which it is confined. The pressure it 

 exerts upon the confining walls depends upon the temperature. A quantity of gas can 

 not be specified by volume only ; all three factors — volume, temperature, and pressure — 

 must be stated. The relations between these three factors are expressed by means of the 

 following equation, 



pv=KT (1) 



in which p, v, and T represent simultaneous values of the pressure, volume, and absolute 

 temperature of any definite quantity of gas, while K is a constant, the numerical value of 

 which depends upon the quantity of gas considered and the units in which pressure, volume, 

 and temperature are measured. 



While the behavior of gases at atmospheric pressure closely approximates the equa- 

 tion (1), the relation is not exact. The expansion of air is nearer one-272d of its volume at 

 273.16°K per degree. For most practical purposes such errors may be neglected. 



If we take weights of gases proportional to their molecular weights, a new relation of 

 the greatest importance develops: The value of the constant in equation (1) is the same 

 for each gas. It is customary to use as the unit of quantity, the mol, the number of grams 

 of gas equal to the molecular weight. When 1 mol is the quantity considered, the resulting 

 value of K is designated R. 



Values of R in PV = RT for one mol of ideal gas.— 1 bar = 10" dyne/cm 2 = 0.987 

 atm. 1 kg/cm 2 = 0.968 atm. Gram molar volume of ideal gas at 0°C = 22,414.1 cm 3 . 

 Pound molar volume of ideal gas at 32°F = 359.05 ft 3 . Ice point, 0°C = 273.16°K ; 

 32°F = 491.7°R. 1 liter = 1000.027 cm 3 . 



Temperature in degrees Rankin, °R (per pound mol) 

 Pressure Volume Energy 



With the mol the unit of quantity, N the number of mol of gas, equation (1) becomes 



pv = NRT (2) 



By the use of equation (2), the above table, and a table of molecular weights, the solution 

 of any problem involving volumes, temperatures, pressures, and weights of gases is 

 very simple. 



Mixtures of gases. — Any quantity of gas fills the space in which it is confined and 

 exerts a pressure upon the confining walls. If an additional quantity is added, the pressure 

 is increased in direct proportion to the quantity added. One can regard the pressure 

 exerted by each portion of the total quantity of gas as independent of the presence of the 

 rest. This is true if the second portion of gas is different chemically from the first (Dalton's 

 law), provided the gases do not react chemically. 



(continued) 



SMITHSONIAN PHYSICAL TABLES 



