SI Units and the Standard-State Pressure

In all previous JANAF Thermochemical Tables, the standard-state pressure was one atmosphere (101 325 Pa) and the unit of energy was the thermochemical calorie (4.184 J). For this publication, the standard-state pressure is changed to one bar (100 000 Pa) and the energy unit to the joule. The values from previous JANAF tabulations have been converted as described below. This information is provided not only to make clear the correspondence between this publication and previous JANAF Thermochemical Tables but also to assist the reader in making comparisons with other tables. This information is the same as that provided in The NBS Tables of Chemical Thermodynamic Proper- 

For the energy units the defined conversion factor of 4.184 J cal is used. 

The following expressions define the effect of pressure on the properties of all substances. 

For the small pressure change from 1 atm to 1 bar, the pressure coefficients may be taken as constants for condensed 

The conversion equations used for the change in standard-state pressure are listed below together with some that apply to thermal functions. Superscript and denote values at 1 bar and 1 atm, respectively. These equations apply to the small change in pressure from 1 atm to 1 bar. 

---