Triple points and critical points

Triple points, critical points and the 1 atm boiling (or sublimation) points of common substances. A substance whose triple-point pressure exceeds 1 atm — such as CO₂ — can only sublime at ordinary pressure.


Water	$\ce{H2O}$	273.160	0.6117	647.096	22.064	373.12	boils	IAPWS-95 / IAPWS-IF97
Carbon dioxide	$\ce{CO2}$	216.592	518	304.128	7.377	194.69	sublimes	Span & Wagner 1996
Ammonia	$\ce{NH3}$	195.495	6.091	405.400	11.333	239.82	boils	Tillner-Roth et al. 1993
Methane	$\ce{CH4}$	90.694	11.7	190.564	4.599	111.67	boils	Setzmann & Wagner 1991
Argon	$\ce{Ar}$	83.806	68.89	150.687	4.863	87.30	boils	Tegeler, Span & Wagner 1999
Oxygen	$\ce{O2}$	54.361	0.1463	154.581	5.043	90.19	boils	Schmidt & Wagner 1985
Nitrogen	$\ce{N2}$	63.151	12.52	126.192	3.396	77.36	boils	Span et al. 2000

Above the critical point there is no boundary between liquid and gas. Water’s triple point, 273.16 K, used to define the kelvin.

Sources

W. Wagner & A. Pruß, J. Phys. Chem. Ref. Data 31, 387 (2002) — IAPWS-95 (water).
R. Span & W. Wagner, J. Phys. Chem. Ref. Data 25, 1509 (1996) — carbon dioxide.
R. Span et al., J. Phys. Chem. Ref. Data 29, 1361 (2000) — nitrogen; R. Schmidt & W. Wagner, Fluid Phase Equilib. 19, 175 (1985) — oxygen; C. Tegeler, R. Span & W. Wagner, J. Phys. Chem. Ref. Data 28, 779 (1999) — argon; U. Setzmann & W. Wagner, J. Phys. Chem. Ref. Data 20, 1061 (1991) — methane; R. Tillner-Roth et al., DKV-Tagungsbericht 20, 167 (1993) — ammonia; as implemented in the NIST Chemistry WebBook.

Sources

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