Exact SI Constants and Derived Values
| Quantity | Symbol | Value | Unit | Status |
|---|
c, h, e, k and NA are exact by definition since the 2019 revision of the SI [1]; gn and the standard atmosphere are exact conventional values [3]. Calculated values follow from them exactly and are rounded here; they match CODATA 2018 [2].
Universal Gas Constant R in Common Units
| R (calculated) | Unit |
|---|
Calculated from R = NAk with exact unit definitions [3]: 1 atm = 101 325 Pa, 1 torr = 1/760 atm (the conventional mmHg is 0.000014 % larger), 1 bar = 105 Pa, 1 cal = 4.184 J, 1 Btu = 1055.05585262 J, 1 lb = 0.45359237 kg, 1 lbf = 1 lb × gn, 1 ft = 0.3048 m, 1 °R = 5/9 K.
Ideal-Gas Properties at 300 K
| Gas | M, g/mol | R, kJ/(kg·K) | R, ft·lbf/(lbm·°R) (calculated) | k = cp/cv | cp, kJ/(kg·K) (calculated) | cv, kJ/(kg·K) (calculated) | cp, Btu/(lbm·°R) (calculated) |
|---|
M and R from Çengel Table A-1 and k at 300 K from Table A-2(a) [4]; cp = kR/(k − 1) and cv = R/(k − 1). † Not in Table A-1: M from Smith, Van Ness and Abbott Table B.1 [5] and R = 8.314462618/M. A dash means Table A-2(a) has no k for that gas.
Critical Constants and Acentric Factor
| Substance | Tc, K | Tc, °R (calculated) | Pc, bar | Pc, psia (calculated) | ω |
|---|
From Smith, Van Ness and Abbott Table B.1 [5]. Air is a mixture, so its row gives pseudo-critical constants.
Standard Atomic Weights
| Element | Symbol | Atomic weight, g/mol |
|---|
Abridged standard atomic weights, IUPAC 2021 [6]; for H, C, N, O and S, whose atomic weight varies in nature, the conventional values. These are the elements the site’s chemistry calculators use.