Water Properties (including isotopologues)

Physical data changes with temperature
Thermodynamic and physical data changes with temperature
Comparative hydride data
Ice data
Spectral data
Seawater
Physicochemical data

Vienna Standard Mean Ocean Water
Tritium

List of physicochemical data concerning water

Property

Data

Absorption coefficient, max.( λ > 180 nm)

Absorption coefficient, min.

12,262 cm⁻¹ (at 2935.5 nm wavelength) [130]

8.11 ˣ 10⁻⁶ ˣ cm⁻¹ (at 344 nmavelength) at 23 °C [3936]

Acentric factor (ω)

H₂O, 0.344 [3762 ]

D₂O, 0.364 [3761]

Activity of pure water

unity

Area, surface covered

19.0 Å² ˣ molecule⁻¹ (monolayer [795 ])
9.65568 Å² ˣ molecule⁻¹(single molecule; calculated from dimensions)

8.84 Å² ˣ molecule⁻¹(single molecule; basal plane of hexagonal ice)

Atmospheric content

19.66 g H₂O kg⁻¹, 0.93 mmol L ⁻¹ (25 °C, 101.325 kPa, relative humidity = 100)

Atomic density

100.000 atoms ˣ nm⁻³(24.52 °C; three atoms per molecule)

Bond energy, average at 0 K

H₂O, 0.5 (H-O-H ·O·+2H·), 458.9 kJ ˣ mol ˣ bond ⁻¹

first O-H bond dissociation energy, 492.2145 kJ ˣ mol⁻¹ [350]

D₂O, 0.5 (D-O-D ·O·+2D·), 466.4 kJ ˣ mol ˣ bond ⁻¹

HDO, (H-O-D H· + ·O-D), 493.336 kJ ˣ mol⁻¹ [350]

Boiling point, 101.325 kPa

H₂O: 100.0 °C ^c1, (212 °F), 373.1243 K (99.9743 °C), see [88]

H₂¹⁶O: 99.97 °C [745]

H₂¹⁷O: 100.08 °C [745]

H₂¹⁸O: 100.15 °C [745]

HDO: 100.74 °C [745]

D₂O: 101.42 °C [70], 374.549 K, 53.039 mol ˣ dm⁻³, 0.033 043 mol ˣ dm⁻³ (gas) [3761]

D₂¹⁶O: 101.40 °C [745]

D₂¹⁸O: 101.54 °C [745]

HTO: 100.8 °C [745]

T₂O: 101.51 °C [745 ]

Bulk modulus (= 1/ β_S, adiabatic)

H₂O: 2.234 GPa (2.234 nN ˣ nm⁻², 25 °C)

D₂O: 2.162 GPa (2.162 nN ˣ nm⁻², 25 °C)

Bulk modulus (K = 1/ β_T, isothermal)

H₂O: 2.174 GPa (2.174 nN ˣ nm⁻², 25 °C); 8.9 GPa (ice Ih, -20 °C, [717])

D₂O: 2.100 GPa (2.100 nN ˣ nm⁻², 25 °C)

CAS registry number

H₂O: 7732−18-5

H₂¹⁸O: 14314-42-2

HDO: 14940-63-7

D₂O: 7789-20-0

HTO: 13670−17-2

T₂O: 14940-65-9

Chemical potential (μ)

see Gibbs energy of formation

Chemical potential, temperature coefficient (dμ/dT) [987 ]
= negative molar entropy (-S)

H₂O (gas): −188.7 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C)
H₂O (liquid): -69.9 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C)
H₂O (solid): -44.8 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C)

Chemical potential, pressure coefficient (dμ/dP) [987]
= molar volume

H₂O (gas): 24,460 J ˣ mol⁻¹ ˣ MPa ⁻¹ (25 °C)
H₂O (liquid): 18.07 J ˣ mol⁻¹ ˣ MPa ⁻¹ (25 °C)
H₂O (solid): 19.73 J ˣ mol⁻¹ ˣ MPa ⁻¹ (25 °C)

Cohesive energy density

H₂O: 2.2973 kJ ˣ cm⁻³ = 2.2973 GPa (= ( ΔH_vap - R T)/ V_M) (25 °C)

D₂O: 2.2164 kJ ˣ cm⁻³ = 2.164 GPa (25 °C)

Internal cohesive pressure

168 MPa (25 °C), (≡ 3.04 kJ ˣ mol⁻¹, 25 °C) [1279]

Color

H₂O: very slight blue color

D₂O: colorless

Combining volumes

O₂:H₂ = 1:2.002 88 (0 °C, 101.325 kPa) [2466 ]; if ideal O₂:H₂ = 1:2

Compressibility, adiabatic (β_S), also called isentropic compressibility

H₂O: 0.4477 GPa ⁻¹ (25 °C) [620 ], 0.5086 G Pa ⁻¹ (0 °C)

1.158 GPa ⁻¹ (-20 °C), 0.2277 GPa ⁻¹ (250 K, 400 MPa) [2089 ]
ice Ih: 0.1142 GPa ⁻¹ (0 °C) ( IAPWS )

D₂O: 0.4625 GPa ⁻¹ (25 °C) [620]

Compressibility, critical (= P_c V_c / R T_c)

H₂O: 0.2294

D₂O: 0.2277

Compressibility, isothermal (β_T),

β_T = -(1/V)(δV/δP)_T = <(ΔV)²>/(k_BTV) [1373b ]

H₂O: 0.4599 GPa⁻¹ (25 °C) [ 507]
ice Ih: 0.1178 GPa⁻¹ (0 °C) ( IAPWS ); 0.069 GPa⁻¹ (−20 °C), [561 ]
gas: 10.03 MPa⁻¹ (100 °C, 101.325 kPa) [540]

D₂O: 0.4763 GPa⁻¹ (25 °C) [507]

Compressibility, isothermal (β_T), minimum

H₂O: 0.4415 GPa⁻¹ at 46.5 °C, calculated from [399 ]

D₂O: 0.4489 GPa⁻¹ at 49.9 °C, calculated from [1454 ]

Compressibility, change with pressure

-0.1152 GPa⁻¹ (25 °C) [1599 ]

Conductivity, electrolytic (κ = 1/ ρ) ( IAPWS)

0.05501 μS ˣ cm⁻¹ (25 °C, [737 ])^h, 18.18 MΩ ˣ cm, 1.2 μS ˣ cm⁻¹ (22 °C, degassed; [711])
ice Ih: ≈ 0.06 μS ˣ cm⁻¹ (-20 °C) [717] (mainly from surface defects)

Conductivity, limiting high frequency electrolytic [2171 ]

0.43 S ˣ cm⁻¹ (≈ 0 °C)
ice Ih: ≈ 0.4 μS ˣ cm⁻¹(≈ 0 °C)

Conductivity, specific (of ions, λ)

H⁺ : λ_H = 349.19 S ˣ cm² ˣ mol⁻¹ (25 °C, [737])

OH⁻ : λ_OH = 199.24 S ˣ cm² ˣ mol⁻¹ (25 °C, [737])

Conductivity, thermal

H₂O: 0.610 W ˣ m⁻¹ ˣ K⁻¹ (25 °C) [IAPWS]; 0.606 502 308 W ˣ m⁻¹ ˣ K⁻¹ (25 °C, 0.1 MPa [ IAPWS] from formula)
ice Ih: 2.4 W ˣ m⁻¹ ˣ K⁻¹ (-20 °C) [717]
gas: 0.025 W ˣ m⁻¹ ˣ K⁻¹ (100 °C, 101.325 kPa) [540]

D₂O: 0.595 W ˣ m⁻¹ ˣ K⁻¹ (25 °C) [IAPWS]

Conductivity, thermal; maximum

H₂O: 0.686 W ˣ m⁻¹ ˣ K⁻¹ at 133 °C, calculated from [1453 ]

D₂O: 0.636 W ˣ m⁻¹ ˣ K⁻¹at 113 °C, calculated from [1453]

Critical point (T_c, P_c, ρ_c, V_c)

H₂O: 647.096 K,^c1 22.064 MPa, 322 kg ˣ m⁻³, 3.1056 cm³ ˣ g⁻¹, 55.9 cm³ ˣ mol⁻¹ ( IAPWS) ^g

D₂O: 643.847 K, 21.671 MPa, 356 kg ˣ m⁻³, 56.3 cm³ ˣ mol⁻¹ ( IAPWS) ^g

density 17.775 55 mol ˣ dm⁻³ (IAPWS); 21.6618 MPa [3761 ]

T₂O: 641.657 K, 21.385 MPa, 376 kg ˣ m⁻³, 58.6 cm³ ˣ mol⁻¹ [830 ]^a

Critical point, second

H₂O: no generally accepted value, for example, ≈ 217 K, ≈ 340 MPa, ≈ 1130 kg ˣ m⁻³ [419 ]; ≈ 188 K, ≈ 230 MPa, ≈ 1100 kg ˣ m⁻³ [432 ]; ≈ 182 K, ≈ 195 MPa [580 ]; 145−175 K, ≈ 200 MPa [999 ]; 223 K, ≈ 50 MPa [1685 ], ≈ 205 K, ≈ 50 MPa [2119 ], ≥ 210 K, 35-50 MPa [2647 ], 197 K, 180 MPa [3734 ]; 220.9 K, 60 MPa [3954 ], 184 K, 173 MPa [4122 ]; 215 K [4311 ]; 190 K 175 MPa [4329 ].

D₂O: no generally accepted value, ≈ -78 °C, ≈ 230 MPa, ≈ 1220 kg m⁻³ [450a]; ≈ -86 °C, ≈ 211 MPa [580]; ≈ -44 °C, ≈ 60 MPa [450b]

Cryoscopic constant

H₂O: 1.8597 K ˣ kg ˣ mol⁻¹

H₂¹⁸O: 2.0636 K ˣ kg ˣ mol⁻¹

D₂O: 2.0224 K ˣ kg ˣ mol⁻¹

Density (25.0 °C, 101.325 kPa)

997.05 kg ˣ m⁻³ [67, 112], 997.047 013 kg ˣ m⁻³ (25 °C, 0.1 MPa [ IAPWS] from formula)

Air saturated water, 997.045 kg ˣ m⁻³ (25 °C, 0.1 MPa) [4165 ]

H₂O

2260 kg ˣ m⁻³(liquid, ≈ 1500 K, 57 GPa) [1218 ]

H₂¹⁷O

1053.12 kg ˣ m⁻³ [1006]

H₂¹⁸O

1109.30 kg ˣ m⁻³ [1006]

HDO

1050.7 kg ˣ m⁻³ [1857 ]

D₂O

1104.36 kg ˣ m⁻³ [620]

D₂¹⁷O

1159.83 kg ˣ m⁻³ [1006]

D₂¹⁸O

1215.22 kg ˣ m⁻³ [1006]

T₂O

1213.28 kg ˣ m⁻³ [1006]

Density of ice at melting point^a

H₂O: 916.72 kg ˣ m⁻³ (0 °C, 101.325 kPa) ( IAPWS )

D₂O: 1017.5 kg ˣ m⁻³ (3.82 °C)

Density of liquid water at melting point [70]

H₂O: 999.84 kg ˣ m⁻³ (0 °C, 101.325 kPa)

D₂O: 1105.46 kg ˣ m⁻³ (3.813 °C)

Density of gas at boiling point

H₂O: 0.5976 kg ˣ m⁻³(100 °C, 101.325 kPa) [540] (compare air 0.9461 kg ˣ m⁻³)

D₂O: 0.033 043 mol ˣ dm⁻³ [3761]

Density of iquid water at boiling point

D₂O: 53.039 mol ˣ dm⁻³ [3761]

Density maximum and molecular volume at the temperature of maximum density [67, 112]

999.974 95 kg ˣ m^{−3 e}

3.984 °C

H₂O

999.972 kg ˣ m⁻³, 29.91 Å ³ mol⁻¹

999.975 kg ˣ m⁻³ ( IAPWS formula)

3.984 °C

3.978 °C ( IAPWS)

H₂¹⁸O

1112.49 kg ˣ m⁻³, 29.87 Å ³ mol⁻¹

4.211 °C

D₂O

1105.3 kg ˣ m⁻³, 30.07 Å ³ mol⁻¹;

55.221 [3761]

11.185 °C,

284.748 [3761]

D₂¹⁸O

1216.88 kg ˣ m⁻³, 30.06 Å ³ mol⁻¹

11.438 °C

T₂O

1215.01 kg ˣ m⁻³, 30.10 Å ³ mol⁻¹

13.403 °C

Dielectric constant (more details)

H₂O: 87.9 (0 °C), 78.4 (25 °C; 78.375 218 [ IAPWS ] from formula at 0.1 MPa), 55.6 (100 °C) [63]
104.3 (supercooled liquid, 240 K, IAPWS )
ice Ih: 99 (-20 °C) 171 (−120 °C) [717]
gas: 1.0059 (100 °C, 101.325 kPa) [540]

D₂O: 78.06 (25 °C) [808 ]

D₂O ice Ih: 104 (-20 °C) [717]

Dielectric, change with pressure

37.88 GPa ⁻¹ (25 °C) [1599]

Dielectric relaxation

H₂O: 8.14 ˣ 10⁻¹²s (25 °C) [2414 ]

H₂O ice Ih: ≈ 2 ˣ 10^-5s (0 °C)

D₂O: 12.3 ˣ 10⁻¹²s (20 °C) [8]

Diffusion coefficient (translational)

H₂O: 0.2299 Å² ˣ ps⁻¹ (25 °C) [1933 ], 0.0187 Å² ˣ ps⁻¹ (−31 °C) [62]; 1 Å² ˣ ps⁻¹ = 10^-8 ˣ m² ˣ s⁻¹

H⁺ : 0.93 Å² ˣ ps⁻¹ (25 °C) [4170 ]

H• : 0.7-0.8 Å² ˣ ps⁻¹ (25 °C) [4170]

OH⁻ : 0.53 Å² ˣ ps⁻¹ (25 °C) [4170]

e⁻: 0.48-0.49 Å² ˣ ps⁻¹ (25 °C) [4170]

OH• : 0.21-0.23 Å² ˣ ps⁻¹ (25 °C) (cf. Cl⁻ : 0.20 Å² ˣ ps⁻¹ (25 °C) [4170]
ice Ih; 6 x 10⁻⁸ Å² ˣ ps⁻¹ ( −20 °C; through interstitial sites) [717 ]
≈ 10^-8 Å² ˣ ps⁻¹ (amorphous water, ≈ 160 K) [ 334]

D₂O: 0.2109 Å² ˣ ps⁻¹ (25 °C) [8]

H₂¹⁸O: 0.266 Å² ˣ ps⁻¹ [745]

HDO: 0.234 Å² ˣ ps⁻¹ [745]

HTO: 0.244 Å² ˣ ps⁻¹ [745]

Diffusion coefficient (rotational)

H_2¹⁷O: 0.104 rad² ˣ ps⁻¹ (25 °C) [2112]

D₂_¹⁷O: 0.086 rad² ˣ ps⁻¹ (25 °C) [2112]

Diffusion coefficient (ions)

H⁺ : 0.931 Å² ˣ ps⁻¹ (25 °C) [2116 ]

OH⁻ : 0.503 Å² ˣ ps⁻¹ (25 °C) [2116]

Diffusivity, thermal

H₂O: 14.6 Å² ˣ ps⁻¹ (25 °C)

D₂O: 12.7 Å ² ˣ ps⁻¹ (25 °C)

Dimer dissociation energy

H₂O, gas: 13.22 kJ ˣ mol⁻¹ (10 K) [2621]

D₂O, gas: 14.88 kJ ˣ mol⁻¹ (10 K) [2621]

Dipole moment (average), μ ^z

H₂O: liquid: 2.95±0.2 D (27 °C) [129]

H₂O: gas: 1.854 98 D ( 6.1875 ˣ 10⁻³⁰ C ˣ m) [IAPWS],
H₂O: ice Ih: 3.09 D [238]

HDO gas: 1.8517 D [IAPWS]

D₂O gas: 1.87 D

Displacement, root mean square

≈ 70 µm s⁻¹ [1577a]

Dissociation constant
= [H₂]²[O₂]/[H₂O]² (dimensionless)

5.2 ˣ 10^-6 (61 MPa, 2700 °C) [2467 ]

Dissociation constant,
= [H⁺][OH⁻]/[H₂O]

H₂O: 1.821 ˣ 10⁻¹⁶ mol ˣ L⁻¹(25 °C) [808]

H₂O ice Ih: 3.8 ˣ 10⁻²² mol ˣ L⁻¹ (−10 °C) [1831 ]

D₂O: 3.54 ˣ 10⁻¹⁷ mol ˣ L⁻¹(25 °C) [808]

D₂O: ice Ih: 1.9 ˣ 10^-23 mol ˣ L⁻¹(−10 °C) [1831]

T₂O: ≈ 1.1 ˣ 10⁻¹⁷ mol ˣ L⁻¹(25 °C) [808]

Dissociation in liquid water, ΔG (25 °C)

2H₂O H₃O⁺ + OH⁻ 79.907 kJ ˣ mol⁻¹ ^j

H-O-H H· + ·O-H see bond energies

2D₂O

D ₃O⁺ + OD⁻ 84.88 kJ ˣ mol⁻¹ ^j

Dissociation rate (25 °C)

H₂O H⁺ + OH⁻ 2.59 ˣ 10⁻⁵ L ˣ mol⁻¹ ˣ s⁻¹H⁺ + OH⁻ H₂O 1.43 ˣ 10¹¹ L² ˣ mol^-2 ˣ s⁻¹

Dissociation thermodynamics (25 °C)

H₂O (liq) H⁺(aq) + OH⁻(aq) [1938 ]

ΔU° = 59.5 kJ ˣ mol⁻¹

ΔV° = 22.13 cm³ ˣ mol⁻¹

ΔH° = 55.8 kJ ˣ mol⁻¹

ΔG° = 79.9 kJ ˣ mol⁻¹

ΔS° = -80.8 J ˣ K⁻¹ ˣ mol⁻¹

Ebullioscopic constant

H₂O: 0.5129 K ˣ kg ˣ mol⁻¹

D₂O: 0.5626 K ˣ kg ˣ mol⁻¹

Electrochemical surface potential

−0.4 V [2256]

Electron affinity [563 ]

H₂O + e⁻ →H₂O⁻ + energy

−16 kJ ˣ mol⁻¹ (-0.17 eV) (25 °C)^l; surface 0.8 ev, bulk 0.1-0.3 ev [3368]
HOMO-LUMO gap, 659 kJ ˣ mol⁻¹ (6.83 eV) (25 °C)

Elemental composition, w/w ^a

H₂O: 88.8097 % oxygen, 11.1903 % hydrogen

HDO: 84.1129 % oxygen, 15.8871 % hydrogen

D₂O: 79.8866 % oxygen, 20.1134 % hydrogen

T₂O: 72.6205 % oxygen, 27.3795 % hydrogen

Energy, internal (U)

liquid: 1.8883 kJ ˣ mol⁻¹ (25 °C, 101.325 kPa) [540 ]
ice Ih: -6.007 kJ ˣ mol⁻¹ (0 °C, 101.325 kPa) ( IAPWS)
gas: 45.15 kJ ˣ mol⁻¹ (100 °C, 101.325 kPa) [540]

Enthalpy (H = U + PV)

1.8909 kJ ˣ mol⁻¹ (25 °C) [67]
ice Ih: -6.005 J ˣ mol⁻¹ (0 °C, 101.325 kPa) ( IAPWS)
gas: 48.20 kJ ˣ mol⁻¹ (100 °C, 101.325 kPa) [540]

Enthalpy of formation, ΔH_f,

H₂O liquid: -286.629 kJ ˣ mol⁻¹ (0 °C) [2052]

ice Ih: -292.639 kJ ˣ mol⁻¹ (0 °C) [2052]

H₂O gas: -241.584 kJ ˣ mol⁻¹ (0 °C) [2052]

D₂O: -294.6 kJ ˣ mol⁻¹ (25 °C) [808]

Enthalpy of vaporization (ΔH_vap, liquid); the latent heat of vaporization

H₂O: 45.051 kJ ˣ mol⁻¹ (0 °C) [906 ], 40.657 kJ ˣ mol⁻¹ (100 °C) [61]; 46.567 kJ ˣ mol⁻¹ (240 K) [906]

D₂O: 45.988 kJ ˣ mol⁻¹ (3.82 °C), 41.521 kJ ˣ mol⁻¹ (101.42 °C), calculated from [1453]

T₂O: ~45.81 kJ ˣ mol⁻¹ (25 °C)

Enthalpy of fusion; the latent heat of fusion

6.00678 kJ ˣ mol⁻¹ (0 °C, 101.325 kPa) [1385 ]
6.354 kJ ˣ mol⁻¹ (81.6 °C, 2150 MPa, ice VI ) [535 ]

H₂¹⁸O: 6.029 kJ ˣ mol⁻¹ (0.31 °C) [1710]

D₂O: 6.132 kJ ˣ mol⁻¹ (3.68 °C) [2000 ]

D₂¹⁶O: 6.315 kJ ˣ mol⁻¹ (3.82 °C) [1710]

HD¹⁶O: 6.227 kJ ˣ mol⁻¹ (2.04 °C) [1710]

Enthalpy of sublimation (ice Ih)

51.059 kJ ˣ mol⁻¹ (0 °C), 51.139 kJ ˣ mol⁻¹ (240 K) [906]

Entropy (S)

liquid, gas, ice Ih; reference state; 0 J ˣ mol⁻¹ ˣ K⁻¹ (exactly, triple point) [2473 ]18.

63.45 J ˣ mol⁻¹ ˣ K⁻¹ (Absolute entropy at triple point) [869 ]
liquid: 6.6177 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [67]

liquid: 367.201 457 J ˣ kg⁻¹ ˣ K⁻¹ (25 °C) (IAPWS) from formula
ice Ih: -21.99 J ˣ mol⁻¹ ˣ K⁻¹ (0 °C) ( IAPWS)

ice Ih: 3.408 J ˣ mol⁻¹ ˣ K⁻¹ (0 K) [1832 ] ≈ RLn(3/2) J ˣ mol⁻¹ ˣ K⁻¹
H₂O, gas: 132.5 J ˣ mol⁻¹ ˣ K⁻¹ (100 °C, 101.325 kPa) [540]

D₂¹⁶O: gas, 216.602 69 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

D₂¹⁷O: gas, 232.179 9 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

D₂¹⁸O: gas, 217.923 64 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

Entropy, molar

see Chemical potential, temperature coefficient (dμ/dT)

Entropy of fusion

H₂O: 22.00 J ˣ mol⁻¹ ˣ K⁻¹ (0 °C) [8]

D₂O: 22.15 J ˣ mol⁻¹ ˣ K⁻¹ (3.68 °C) [2000]

Entropy of vaporization [8]

108.951 J ˣ mol⁻¹ ˣ K⁻¹ (100 °C)

Evaporation coefficient (α) ⁿ

in dispute: 1.0 (25 °C) [2326 ]; 0.65 (25 °C) [2327 ]; 0.13 (20 °C) [2325 ]

Expansion coefficient (α),

α_P = (1/V)(δV/δT)_P = <(ΔV)(ΔS)>P/(k_B²T) [1373b]

H₂O: 0.000000 °C⁻¹(3.984 °C), 0.000 253 °C⁻¹ (25 °C) [68]

−0.000 059 °C⁻¹ (0 °C), −0.002963 (-20 °C),

+0.0004930 (250 K, 400 MPa) [2089]
ice Ih: 0.000 1598 °C⁻¹ (0 °C, 101.325 kPa) (IAPWS );

0.000 053 °C⁻¹ (-20 °C) [717]

D₂O: 0.000 1722 °C⁻¹(25 °C) [620]

liquid D₂O: −0.000 032 °C⁻¹(3.81 °C)

solid D₂O: 0.000 139 °C⁻¹(3.81 °C)

Fractional dissociation
= ([H₂]+½[O₂])/([H₂]+½[O₂]+[H₂O])

0.014 (61 MPa, 2700 °C) [2467]

Fragile to strong liquid transition

≈ 220 K [1200]

Freezing point, 101.325 kPa

25 °C

< 0 °C (see also melting point)

> 960.1 MPa (to ice VI)

Gas constant (R_S)

= R /molar mass = 461.52309 J ˣ kg⁻¹ ˣ K⁻¹

Gas constant (R⁹⁵)

461.518 05 J ˣ kg⁻¹ ˣ K⁻¹ ( IAPWS)

kT/V_molecule ; RT/V_mole

137.581 MPa (25 °C)

Gibbs energy (G = U - TS + PV), all referenced to triple point

liquid: -82.157 J ˣ mol⁻¹(25 °C, 101.325 kPa) [540]

liquid: -4561.7537 J ˣ kg⁻¹(25 °C, 101.325 kPa) (IAPWS) from formula
ice Ih: 1.826 J ˣ mol⁻¹(0 °C, 101.325 kPa) (IAPWS)
gas: −1239 J ˣ mol⁻¹(100 °C, 101.325 kPa) [540]

Gibbs energy (total)

liquid: -6.78442 kJ ˣ mol⁻¹ (25 °C, 101.325 kPa) [2254 ]

Gibbs energy of formation, ΔG_f,
= Chemical potential (μ)

H₂O (liquid): -237.18 kJ ˣ mol⁻¹ (25 °C) [987]
H₂O (gas): -228.59 kJ ˣ mol⁻¹ (25 °C) [987]
H₂O (solid): -236.59 kJ ˣ mol⁻¹ (25 °C) [987]

HDO (liquid): -241.86 kJ ˣ mol⁻¹ (25 °C) [988 ]
HDO (gas): -233.11 kJ ˣ mol⁻¹ (25 °C) [988]

D₂O (liquid): -243.44 kJ ˣ mol⁻¹ (25 °C) [988]
D₂O (gas): -234.54 kJ ˣ mol⁻¹ (25 °C) [988]

Glass transition temperature

Low-density liquid (≈ 0.1 MPa): 136 K (subject to dispute [312, 2593])

High-density liquid (≈ 0.1 MPa): 116 K; 140 K at 0.2 GPa [2048]

Very high-density liquid (1 GPa); 122 K [2209]

Hardness (Mohs scale)

ice Ih: variable ≈ 2 (0 °C), ≈ 6 (-50 ≈ -78.5 °C) [2097],

often reported as = 1.5

Heat capacity ratio (γ=C_P/C_V)

H₂O (gas): 1.3368 (100 °C, 101.325 kPa) [540]

Helmholtz energy (A = U - TS) [540]

liquid: -83.989 J ˣ mol⁻¹ (25 °C, 101.325 kPa)
ice Ih: -0.166 J ˣ mol⁻¹ (0 °C, 101.325 kPa) ( IAPWS)
gas: -4293 J ˣ mol⁻¹ (100 °C, 101.325 kPa)

Hexadecapole moments [2233]

γ_xxxx = -0.46 D ˣ Å^3,γ_yyyy = 1.53 D ˣ Å³, γ_zzzz = −1.43 D ˣ Å³ (calculated for a single molecule)

Hydrogen bond

Donor, Σα 1.17 [666 ]; compare CHCl₃, 0.15; CH₃OH, 0.43
Acceptor, Σβ; 0.47 [666]; compare (C₂H₅)₂O, 0.41; CH₃OH, 0.47

Donor number (D_N), 18.0 [456 ]; compare CH₃CN 14.1; CH₃OH, 19.0
Acceptor number (A_N), 54.8 [456]; compare C₆H₆ 8.2; CH₃OH, 41.3

Donor acidity = 1.062; 20 °C [2892 ]

Acceptor basicity = 0.025; cf tetramethylguanidine = 1.000; 20 °C [2892]

Dipolarity = 0.997; cf dimethylsulfoxide = 1.000; 20 °C [2892]

Polarizability; 0.681 cf carbon disulfide = 1.000; 20 °C [2892]

Hygroscopicity

liquid; D₂O > H₂O

Ionic mobility

H⁺ : 36.23 ˣ 10^-8 m² ˣ s⁻¹ ˣ V ⁻¹(25 °C) [2116]

OH⁻: 20.64 ˣ 10^-8 m² ˣ s⁻¹ ˣ V ⁻¹ (25 °C) [2116]

Ionization potential (relative vacuum)

H₂O + energy → H₂O·⁺+ e⁻

H₂O: gas; 1216 kJ ˣ mol⁻¹ (12.61 eV) [381a ]; 101,766.3 cm⁻¹ [2571 ]

2^nd 14.73 ev, 3^rd 16.2 ev, 4^th 18.0 ev
H₂O: liquid; 1018 kJ ˣ mol⁻¹ (10.56 eV) [381a], Latest estimates, ≈ 10.0 ev [3368 ], 9.7 ev relative vacuum, 5.14 ev relative the standard hydrogen electrode [3382 ]
H₂O: ice; 1061 kJ ˣ mol⁻¹ (11.00 eV) [381a]

HDO: gas; 101,840.1 cm⁻¹ [2571]

D₂O: gas 1219 kJ ˣ mol⁻¹ (12.64 eV) [381b]; 101,915.2 cm⁻¹ [2571]

Vertical ionization energy, [3852 ]

H₂O: liquid; the ion is in the same geometry as the neutral; 11.67 ev

Adiabatic ionization energy, [3852]

H₂O: liquid; the ion is in its lowest energy, with relaxed geometry; 10.12 ev

Joule-Thomson coefficient (25 °C)

0.214 K MPa ⁻¹ [ IAPWS]

K_w (ion product)

H₂O: 1.012 ˣ 10⁻¹⁴ (25 °C)

D₂O: 1.352 ˣ 10⁻¹⁵ (25 °C)

T₂O: ~6 ˣ 10⁻¹⁶ (25 °C)

Lifetime

≈ 1 ms

Limits of stability for liquid water

Lowest temperature, -21.985 °C at 209.9 MPa
Lowest pressure, 611.657 Pa at 0.01 °C
Lowest density, 0.322 g cm⁻³ at 373.946 °C, 22.064 MPa
Highest temperature, 373.946 °C, >22.064 MPa
Highest pressure, ≈ 12 GPa at 373.946 °C
Highest density, ≈ 1.7 g cm⁻³ at 373.946 °C, ≈ 12 GPa

LogP

D₂O: −1.38

Magnetic susceptibility [670 ]

−1.64 ˣ 10⁻¹⁰ m³ ˣ mol⁻¹(25 °C), −1.63x10⁻¹⁰ m³ ˣ mol⁻¹(0 °C)

Magnetic susceptibility, dimensionless (χ)

9.04 ˣ 10^-6(20 °C) [3591 ]

Mass spectrum

H₂O⁺ (1.0), OH⁺ (0.32), H⁺ (0.26), O⁺ (0.07), O²⁺ (0.002), H₂⁺ (0.001) (ionization cross sections at 200 eV relative to H₂O⁺, [1456 ])

Melting, contraction on, at melting point

H₂O: 1.634 cm³ ˣ mol ⁻¹(0 °C)

D₂O: 1.567 cm³ ˣ mol ⁻¹(3.82 °C)

Melting point, 101.325 kPa [70, 88]

H₂O: 0.00 °C ^c2, (32 °F), 273.152 519 K ( IAPWS)

¹H₂¹⁶O: 0.3 °C (D/H = 4.2 ppm,¹⁸O = 910 ppm) [2728 ]

1410 K at 72 GPa [2096 ]

HDO: 2.04 °C, 275.19

D₂O: 3.82 °C

T₂O: 4.49 °C

H₂¹⁸O: 273.43 K [829 ]

Melting point, 25 °C

H₂O: 960.1 MPa (to ice VI)

D₂O: ≈ 1 GPa (to ice VI)

Melting point, pressure coefficient

H₂O: -74.293 mK ˣ MPa ⁻¹(0 °C) [1385]

D₂O: -68 mK MPa ⁻¹(3.82 °C)

Molality ^b

H₂O: 55.508 472 mol ˣ kg⁻¹

D₂O: 49.931 324 mol ˣ kg⁻¹

Molar concentration ^b

H₂O: 55.345 mol ˣ L⁻¹(25 °C)

HOD: 55.244 mol ˣ L⁻¹(25 °C, but maximum possible is 27.3 mol ˣ L⁻¹) [1857]

D₂O: 55.142 mol ˣ L⁻¹(25 °C)

Molar isotopic composition ^a,^m

Molar masses may be calculated
e⁻	5.485 799 058 ˣ 10^-4 g ˣ mol⁻¹
H⁺ (p)	1.007 276 461 g ˣ mol⁻¹
n	1.008 664 909 g ˣ mol⁻¹
H	1.007 825 032 23 g ˣ mol⁻¹
D	2.014 101 778 12 g ˣ mol⁻¹
T	3.016 049 277 9 g ˣ mol⁻¹
¹⁶O	15.994 914 619 57 g ˣ mol⁻¹
¹⁷O	16.999 131 756 50 g ˣ mol⁻¹
¹⁸O	17.999 159 612 86 g ˣ mol⁻¹

H₂¹⁶O

99.7317 % (55.21 M, 25 °C)

18.010 564 69 g ˣ mol⁻¹

H₂¹⁷O

0.037 1884 % (19.51 mM, 25 °C)

19.014 781 56 g ˣ mol⁻¹

H₂¹⁸O

0.199 983 % (99.62 mM, 25 °C)

20.014 8105 g ˣ mol⁻¹

HD¹⁶O

0.031 0693 % (16.29 mM, 25 °C)

19.016 841 43 g ˣ mol⁻¹

HD¹⁷O

1.15 853 ˣ 10⁻⁵ % (5.8 µM, 25 °C)

20.021 058 31 g ˣ mol⁻¹

HD¹⁸O

6.23 003 ˣ 10⁻⁵ % (29.5 µM, 25 °C)

21.021 0872 g ˣ mol⁻¹

D₂¹⁶O

2.6 ˣ 10⁻⁶ % (1.3 µM, 25 °C)

20.023 118 18 g ˣ mol⁻¹

D₂¹⁷O

9 ˣ 10⁻¹⁰ % (5 nM, 25 °C)

21.027 335 06 g ˣ mol⁻¹

D₂¹⁸O

4.9 ˣ 10⁻⁹ % (26 nM, 25 °C)

22.027 363 96 g ˣ mol⁻¹

HT¹⁶O

4.987 ˣ 10⁻¹⁷ % ^f

20.018 788 92 g ˣ mol⁻¹

DT¹⁶O

7.7685 ˣ 10⁻²¹%

21.025 066 g ˣ mol⁻¹

T₂¹⁶O

6.235 ˣ 10⁻³⁴ % ^f

22.027 013 16 g ˣ mol⁻¹

T₂¹⁸O

1.25 ˣ 10⁻³⁶ % ^f

24.031 258 g ˣ mol⁻¹

Molar mass^b

H₂O: 18.015 268 g ˣ mol⁻¹ (compare molar mass of dry air 28.965 46 g ˣ mol⁻¹ [2215 ])

D₂O: 20.027 508 g ˣ mol⁻¹ (IAPWS)

Molar volume (gas, STP)

0.022 199 m³ ˣ mol⁻¹ (0 °C, 101.325 kPa)

Molar volume (liquid)

see Volume, molar

Molecular dimensions

O-H bond length (liquid, ab initio), 0.991 Å [90]

O-H bond length (liquid, by diffraction), 0.990 Å [1884 ]

O-H bond length (solid ice Ih, -20 °C), 0.985 Å [717]

O-H bond length (gas, 0 K, calc.), 0.957 85 Å [836 ], 0.9765 Å [2441 ]

O-H root mean square amplitude (gas, 0 K, calc.) 0.0690 Å [2441]

H H root mean square amplitude (gas, 0 K, calc.) 0.1142 Å [2441]

H-O-H bond angle (liquid, ab initio), 105.5° [90]

H-O-H bond angle (solid ice Ih, -20 °C), 106.6°±1.5° [717]

H-O-H bond angle (gas, 0 K, calc.), 104.50° [836] 104.43° [2441]

O···O (liquid, ≈ 20 °C), average 2.81 Å, most probable 2.70 Å [2120 ]

O···O (ice, −16.8 °C), average 2.76 Å, most probable 2.71 Å, [2120]

O···O (gas, 100 °C), average 36.85 Å

O-D bond length (liquid), 0.970 Å [91], 0.985 Å [1884]

O-D bond length (gas, 0 K, calc.), 0.95783 Å [836], 0.97077 Å [2441]

O-D root mean square amplitude (gas, 0 K, calc.) 0.0586 Å [2441]

D D root mean square amplitude (gas, 0 K, calc.) 0.0960 Å [2441]

D-O-D bond angle (liquid), 106° [91]

D-O-D bond angle (gas, 0 K, calc.), 104.49° [836], 104.408° [2441]

O···O···O bond angle (solid, ice Ih), 109.47°

Molecular force constants (gas, [2445 ])

432.47 kJ ˣ mol⁻¹ ˣ rad⁻²

5,096.32 kJ ˣ mol⁻¹ ˣ Å⁻²

-57.116 kJ ˣ mol⁻¹ ˣ Å⁻²

226.05 kJ ˣ mol⁻¹ ˣ Å⁻¹ ˣ rad⁻¹

Molecular mass

H₂O:^b 2.991 5051 ˣ 10^-23 g ˣ molecule⁻¹

H₂¹⁶O: 2.990 7243 ˣ 10^-23 g ˣ molecule⁻¹

D₂¹⁶O: 3.324 9166 ˣ 10^-23 g ˣ molecule⁻¹

Moment of inertia (axes through centers of mass)

H₂O: 1.0220 ˣ 10^-40 g ˣ cm²^x; 2.9376 ˣ 10^-40 g ˣ cm² ^y; 1.9187 ˣ 10^-40 g cm² ^z [8]. The SI unit of moment of inertia is kg ˣ m² (= 10⁷ g ˣ cm²)

HDO: 1.2092 ˣ 10^-40 g ˣ cm² ^x; 4.2715 ˣ 10^-40 g ˣ cm² ^y; 3.0654 ˣ 10^-40 g ˣ cm² ^z [8] (z and x axes rotated around y axis by 21.09°)

D₂O: 1.8384 ˣ 10^-40 g ˣ cm²^x; 5.6698 ˣ 10^-40 g ˣ cm²^y; 3.8340 ˣ 10^-40 g ˣ cm²^z [8]

Systematic name for water

Oxidane ( IUPAC) is not used. The preferred name is 'water'

¹H₂O is also known as protium oxide, when distinguishing isotopologues

HDO: 'Semiheavy water'

D₂O: deuterium oxide ('heavy water')

HTO: tritiated water, also sometimes called 'super heavy water'

T₂O: tritium oxide ('super heavy water')

Common 'hoax' name for water

Dihydrogen monoxide (DHMO)

Neutron scattering data, [2551 ]

Coherent scattering length; H, −3.7409 fm; ¹H, −3.7423 fm; ²H (D), +6.674 fm;; ³H (T), +4.792 fm;O, +5.805 fm; ¹⁶O, +5.805 fm; ¹⁷O, +5.867 fm; ¹⁸O, +6.009 fm

Incoherent scattering cross section; H, 80.26 b; ¹H 80.27 b; ²H (D) 2.05 b; ³H (T), +0.14 b; ¹⁶O 0.0 b; ¹⁷O 0.004 b; ¹⁸O 0.0 b

NMR chemical shift, proton

H₂O liquid: 4.82 ppm
H₂O ice: ≈ 7 ppm
H₂O gas: 0.56 ppm, relative to methane [850 ]

HOD gas: ²Δ¹H(HOH, HOD) = -0.040 ppm [4034 ]
4.766 ppm for HDO in D₂O (25 °C, a triplet [609]; relative to sodium 2,2-dimethyl-2-silapentane-5-sulfonate, DSS)

NMR chemical shift, ¹⁷O

H₂O liquid: 287.5 ppm (300 K, relative to O⁸⁺) [886 ]
H₂O gas: 323.6 ppm (300 K, relative to O⁸⁺) [886]

HOD gas: ¹Δ¹⁷O(H₂O, HOD) = −1.51 ppm [4034]

D ₂O gas: ¹Δ¹⁷O(HOD, D₂O) = −1.48 ppm [4034]
D ₂O liquid: 3.08 ppm (relative to H₂O)

Nuclear shielding constants (27 °C), [740 ]

¹H σ(l) 25.79 ppm (44.0 ppm parallel to O—H bond; 16.6 ppm perpendicular to O—H bond, [430 ]); gas to liquid shift, δ = σ(l) - σ(g) = -4.26 ppm
¹⁷O σ(l) 287.5 ppm; gas to liquid shift, δ = σ(l) - σ(g) = −36.1 ppm

NMR spin-spin coupling

Isolated H₂¹⁷O; ¹J(¹⁷O,¹H) = -78.2 Hz [3412 ]

Octupole moment, 25 °C [452 ]

−1.754 D ˣ Å² ^xxz; -0.554 D ˣ Å² ^yyz; −1.981 D ˣ Å² ^zzz

Octupole moment, (alternative)

linear (Ω₀) −1.34 D ˣ Å²; cubic (Ω₂) 1.15 D ˣ Å²; SSDQO1 [1731 ] ^Ω

Optical permittivity (ε_∞) [296 K, 1563]

H₂O: 2.34

H₂¹⁸O: 2.28

D₂O: 2.29

Packing density (volume, O···O 2.82 Å, 4 °C)

0.3925

Oxygen spin-lattice relaxation time

¹⁷O: 6.9 ms ( 25 °C) [2414]

D₂O: 7.43 (25 °C) (based on [70])

pHD

HDO: 7.266 (25 °C)

H₂O: 6.9976 (25 °C; [H₃O]⁺=[OH]⁻ = 1.0054x10^-7 mol ˣ L⁻¹; [IAPWS])

HTO: 7.46 (25 °C) [2621]

Penetration depth, thickness to drop power by 50%, from [130]

minimum: 565 nm (at λ = 2935.5 nm)

maximum: 156.8 m (at λ = 417.5 nm)

Piezoscopic constant (= R/V_m)

H₂O: 0.4602 MPa ˣ K⁻¹ (25 °C)

D₂O: 0.4585 MPa ˣ K⁻¹(25 °C)

T₂O: 0.4580 MPa ˣ K⁻¹ (25 °C)

pK_a and pK_b

pK_a H₂O: (= pK_b H₂O) = 13.995 (25 °C) [2965]

pK_a H₃O⁺: (= pK_bOH⁻) = 0.0 (exactly and invariant of temperature) [2967 ]

pK_a D₂O: (= pK_b D₂O) = 14.869 (25 °C) (based on [70])

pK_a D₃O⁺: (= pK_bOD⁻) = 0.0 (exactly and invariant of temperature)

pK_w

H₂O: 13.995 (25 °C)[IAPWS]

D₂O: 14.869 (25 °C) [70]

T₂O: 1.352 ˣ 10⁻¹⁵ (25 °C)

Polarity/dipolarity, π [666]

1.09

Polarizability, ()

1.636 ˣ 10^-40 F ˣ m²

Polarizability volume,

1.470 Å³; 1.5284 Å³ ^x; 1.4146 Å³ ^y; 1.4679 Å³ ^z [736]
1.457 Å³ (electronic), 0.037 Å³ (static) [IAPWS]

O-atom (1.4146 Å³) H-atoms (0.0836 Å³) [736]

Prandtl Number
(Pr = kinematic viscosity / thermal diffusivity)

H₂O: 6.12 (25 °C)

D₂O: 7.81 (25 °C)

Proton spin-lattice relaxation time (25 °C)

T₁ = 3.6 ± 0.2 s [2098 ]; 3.59 s [2335 ]

Proton spin-spin relaxation time (25 °C)

T₂ = 1.86 ± 0.07 s [2098]; 3.59 s [2335]

Quadrupole moment, Q, 25 °C

-4.27 D ˣ Å ^xx; -7.99 D ˣ Å ^yy; -5.94 D ˣ Å ^zz (calc., liquid H₂O [453 ])

Quadrupole moment (alternative)

linear (Θ₀) 0.28 D ˣ Å; square (Θ₂) 2.13 D ˣ Å; SSDQO1 [1731] ^Ω

Redox: water oxidation
Redox: water reduction

2H₂O O₂(g) + 4H⁺ + 4e⁻ -E° = −1.229 V (25 °C, pH 0)
2H₂O + 2e⁻ H ₂(g) + 2OH⁻ E° = -0.8277 V (25 °C, pH 14)

Refractive index

H₂O: 1.332 86 (25 °C, λ = 589.26 nm) [310]
ice Ih: η^O 1.3091; η^E 1.3105 (−3.6 °C, λ = 589 nm) [717]

D₂O:1.328 28 (20 °C, λ = 589 nm) [795]

Refractive index, real n and imaginary parts k

H₂O: n 1.306169; k 0.300352153 (25 °C, v, 3404.795 cm⁻¹) [942]

D₂O: n 1.342528; k 0.279696327 (25 °C, v, 2503.923 cm⁻¹) [942]

Resistance, electrical (ρ = 1/ κ )

18.18 MΩ ˣ cm (25 °C, pH 6.9976, ultrapure water [737])^h, 0.8 MΩ ˣ cm (22 °C, degassed; [711 ])

Shear modulus (adiabatic elasticity)

H₂O: 2.44 GPa (2.44 nN ˣ nm^-2, 25 °C) [1326 ]

D₂O: 2.50 GPa (2.50 nN ˣ nm^-2, 25 °C) [1326]

Specific heat capacity,

C_P = (δH/δT)_P= T(δS/δT)_P = <(ΔS)²>/k_B [1373b]

H₂O: liquid, 75.338 J ˣ mol⁻¹ ˣ K⁻¹; 4.1819 kJ ˣ kg⁻¹ ˣ K⁻¹,^e2 4.1696 MJ ˣ m⁻³ ˣ K⁻¹ (25 °C, 101.325 kPa, calculated from [1154 ]), 4.181 446 18 kJ ˣ kg⁻¹ K⁻¹ (25 °C, 0.1 MPa [IAPWS] from formula)
108.048 J ˣ mol⁻¹ ˣ K⁻¹ (-20 °C), 67.687 J ˣ mol⁻¹ ˣ K⁻¹ (250 K, 400 MPa) [2089]
ice Ih: 37.77 J ˣ mol⁻¹ ˣ K⁻¹ (0 °C) ( IAPWS ), 22.10 J ˣ mol⁻¹ ˣ K⁻¹ (150 K) [906]
gas: 37.47 J ˣ mol⁻¹ ˣ K⁻¹ (100 °C, 101.325 kPa) [540]

D₂O: liquid, 84.67 J ˣ mol⁻¹ ˣ K⁻¹; 4.228 kJ ˣ kg⁻¹ ˣ K⁻¹,

4.669 MJ ˣ m⁻³ ˣ K⁻¹ (25 °C, calculated from [620])

D₂O: gas, 34.226 118 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

D₂¹⁶O: gas, 34.282 80 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124 ]

D₂¹⁷O: gas, 34.296 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

D₂¹⁸O: gas, 34.307 17 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [4124]

Specific heat capacity minimum, C_P,min

H₂O: 75.27 J ˣ mol⁻¹ ˣ K⁻¹ at 36 °C, calculated from [1453]

D₂O: 82.58 J ˣ mol⁻¹ ˣ K⁻¹ at 61 °C, calculated from [2000]

Specific heat capacity maximum, C_P,min

H₂O: gas 59.6 J ˣ mol⁻¹ ˣ K⁻¹ at ~4700 K [4125 ]

D₂O: gas 59.8 J ˣ mol⁻¹ ˣ K⁻¹ at ~4200 K [4124]

Specific heat capacity, C_v = (∂U/∂T)_v

H₂O: 74.539 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [67]
gas: 28.03 J ˣ mol⁻¹ ˣ K⁻¹ (100 °C, 101.325 kPa) [540]

D₂O: 84.42 J ˣ mol⁻¹ ˣ K⁻¹ (25 °C) [620]; 83.383 9128 J ˣ mol⁻¹ ˣ K⁻¹ (27 °C, 52.912 3711 kPa) (IAPWS)

Speed of sound

H₂O: 1496.7 m ˣ s⁻¹ (25 °C) [620], 1496.699 22 m ˣ s⁻¹ (25 °C, 0.1 MPa [IAPWS] from formula); 'fast' sound ≈ 3200 m ˣ s⁻¹ [1151 ]

1134.6 m ˣ s⁻¹ (-20 °C), 2015.9 m ˣ s⁻¹ (250 K, 400 MPa) [2089]

ice Ih: 3837.9 m ˣ s⁻¹ (0 °C) [1812 ]
gas: 472.2 m ˣ s⁻¹ (100 °C, 101.325 kPa) [540]

D₂O: 1399.2 m ˣ s⁻¹ (25 °C)

Speed of sound, maximum

H₂O: 1555.4 m ˣ s⁻¹ at 74.0 °C, calculated from [921 ]

D₂O: 1461.0 m ˣ s⁻¹ at 75.6 °C, calculated from [1454]

Standard state of water

unity (exactly, as pure solvent); unit molal (as solute)

Sublimation coefficient ⁿ

ice: 1.0 (<194 K); 0.146 (263 K) [2328 ]

Surface density

H₂O (liquid): 10.4 nm^-2(0 °C) [2302]

H₂O (ice Ih): 9.7 nm^-2 (0 °C) [2302]

Surface entropy (= -dγ/dT)

H₂O (liquid - gas): 0.14 mJ ˣ m^-2 ˣ K⁻¹ (0 °C) [2302]

H₂O (ice Ih - liquid): -0.05 mJ ˣ m^-2 ˣ K⁻¹ (0 °C) [2302]

H₂O (ice Ih - gas); 0.26 mJ ˣ m^-2 ˣ K⁻¹ (0 °C) [2302]

Surface enthalpy (surface energy)

H₂O (liquid - gas): 114 mJ ˣ m^-2 (0 °C) [2302]

H₂O (ice Ih - liquid): 15 mJ ˣ m^-2 (0 °C) [2302]

H₂O (ice Ih - gas); 140 mJ ˣ m^-2 (0 °C) [2302]

Supercooled H₂O: 78.8 mJ ˣ m^-2 (−17.3 °C) [2271 ]

Polycrystalline ice Ih: 103.7 mJ ˣ m^-2 (−17.3 °C) [2271]

Surface tension (change with pressure)

H₂O: 6.96 Å (25 °C) (calculated from [1279] and IAPWS )

Surface tension ()

also, Surface energy

H₂O (liquid - gas): 0.07198 N ˣ m⁻¹ (25 °C; 71.98 mJ ˣ m^-2) [IAPWS]

H₂O (liquid - gas): 0.0756 N ˣ m⁻¹(0 °C; 75.6 mJ ˣ m^-2)

H₂O (ice Ih - liquid, γ_sl); 0.0396 N ˣ m⁻¹ (0 °C; 0.0396 J ˣ m^-2) [2103 ]; 0.0291 N ˣ m⁻¹(0 °C; 29.1 mJ ˣ m^-2) [2302 ]

H₂O (ice Ih - gas, γ_sg); 0.0692 N ˣ m⁻¹ (0 °C; 69.2 mJ ˣ m^-2) [2302]

HDO: 0.07193 N ˣ m⁻¹ (25 °C; 0.07193 J ˣ m^-2)

D₂O: 0.07187 N ˣ m⁻¹(25 °C; 0.07187 J ˣ m^-2) [IAPWS]

Surface tension (complex)

H₂O: 0.073 +i( 0.017) N ˣ m⁻¹ (room temperature) [2155 ]

Surface thickness, from ellipsometry

H₂O-air: 0.449 nm (14.5 °C) [2399 ]

Tensile strength

H₂O: −33.3 ± 2.8 MPa (20 °C) [2313 ]

ice Ih ; 1 - 2 MPa (-10 °C)

Triple point

H₂O: 0.01 °C (273.16 K) ^d for VSMOW ^a, 611.654 771 007 894 Pa (IAPWS) from formula, 0.99978 g ˣ cm⁻³ (liquid) [ 536], 0.00485 kg ˣ m⁻³ (gas), 0.91668 g ˣ cm⁻³ (solid, estimated)

H₂¹⁶O: 0.0087 °C [565 ]

H₂¹⁷O: 0.21 °C [745]

H₂¹⁸O: 0.31 °C [717

HD¹⁶O: 2.04 °C [1710]

D₂O: 276.969 K, 660.096 Pa, 1.1056 g cm⁻³ (liquid) [IAPWS], 0.00575 kg ˣ m⁻³ (gas); 276.969 K, 661.59 Pa, 55.188 mol ˣ dm⁻³, 0.000 287 mol ˣ dm⁻³ (gas) [3761]

D₂¹⁶O: 3.82 °C [1710]

D₂¹⁸O: 4.13 °C [745]

HTO: 2.4 °C [745]

T₂O: 4.49 °C [716 ], 662.9 Pa [830]

Van der Waals gas constants [70] ^k

a = 0.5536 Pa (m³ mol⁻¹)²; b = 3.049 ˣ 10^-5 m³ mol⁻¹

Vapor pressure

H₂O: 3.165 kPa (25 °C) [808]; 611.657 Pa (273.16 K, M.Pt.) [906]
H₂O: 37.667 Pa (240 K) [906]
ice Ih: 611.657 Pa (273.16 K), 27.272 Pa (240 K) [906]

D₂O: 2.734 kPa (25 °C) [808]; 659.893 Pa (276.95 K, M.Pt.) [1790 ]

T₂O: 2.639 kPa (25 °C) [808]; 662.388 Pa (277.64 K, M.Pt.) [1790]

Velocity, root mean square

642.5 m s⁻¹ (gas, 25 °C) [2467]

Virial coefficient

H₂O: 991 cm³ mol⁻¹ (gas, 25 °C, saturated vapor pressure) [2316 ]

D₂O: 1089 cm³ mol⁻¹ (gas, 25 °C, saturated vapor pressure) [2316]

Viscosity, dynamic

H₂O: 0.8909 mPa ˣ s (25 °C, 101.325 kPa) 1.0016 mPa ˣ s (20 °C, 101.325 kPa) [IAPWS], 0.889 996 774 mPa ˣ s (25 °C, 0.1 MPa [IAPWS] from formula);
gas: 0.0123 mPa ˣ s (100 °C, 101.325 kPa) [540]

H₂¹⁶O: 1.0016 mPa ˣ s (20 °C) [745]

H₂¹⁸O: 1.0564 mPa ˣ s (20 °C) [745]

HDO: 1.1248 mPa ˣ s (20 °C) [745]

D₂O: 1.095 mPa ˣ s (25 °C) [IAPWS]

D₂¹⁶O: 1.2467 mPa ˣ s (20 °C) [745]

D₂¹⁸O: 1.3050 mPa ˣ s (20 °C) [745]

T₂O: 1.40 mPa ˣ s (estimated, 20 °C) [73 ]

Viscosity, kinematic

H₂O: 0.008935 stoke; 0.8935 ˣ 10^-6 m² ˣ s⁻¹(25 °C)

D₂O: 0.009915 stoke; 0.9915 ˣ 10^-6 m² ˣ s⁻¹(25 °C)

Viscosity, bulk (volume viscosity)

2.47 mPa ˣ s (25 °C) [1703]

Viscosity, temperature coefficient

0.0199 mPa ˣ s ˣ K ⁻¹ (25 °C) [304]

Volume, molar, 101.325 kPa, V_M,
see also chemical potential, pressure coefficient (dμ/dP)

H₂O liquid: 18.0182 cm³ (0 °C) 18.0685 cm³ (25 °C) [1006 ]

H₂O liquid: 18.016 cm³ (3.98 °C)

solid; 19.66 cm³(ice Ih, 0 °C);

gas; 0.030 143 m³(100 °C), 0.781 m³(25 °C, 3.1698 kPa)

H₂O: 50.6 Å³ ˣ molecule⁻¹ from the van der Waals gas 'b' constant

H₂¹⁷O: 18.0556 cm³ (25 °C) [1006]

H₂¹⁸O: 18.0428 cm³ (25 °C) [1006]

HDO: 18.101 cm³ (25 °C) [1857]

D₂O: liquid 18.1331 cm³ (25 °C) [1006]

D₂O: liquid 18.110 cm³ (11.23 °C)

D₂O: solid 19.679 cm³ (3.81 °C) [2838]

D₂¹⁷O: 18.1297 cm³ (25 °C) [1006]

D₂¹⁸O: 18.1263 cm³ (25 °C) [1006]

T₂O: 18.1549 cm³ (25 °C) [1006]

Volume, hydrodynamic (H₂O)₄

72 cm³ ˣ mol⁻¹ [2654 ]

Volume, intrinsic H₂O

mickey mouse ears, 11.01 Å³; if spherical, 14.6 Å³

Volume, molecular H₂O at 101.325 kPa

29.92 Å³ (0 °C); 32.53 Å ³(ice Ih, -20 °C, [717]); 50.05 nm³(gas, 100 °C)

Volume, H₃O⁺ from crystals

26.63 Å³

Volume, OH⁻ from crystals

32 Å³

Volume, van der Waals

14.6 Å³ ˣ molecule⁻¹ (liquid)

50.6 Å³ ˣ molecule⁻¹ (gas, calculated from the Van der Waals gas constants)

Young's modulus

stiffness = stress/strain; ice Ih ~9.42 GPa (-16 °C, disputed) [also 2943 ]

Zero-point energy

H₂O: (liquid, 25 °C) 13.9 kJ ˣ mol⁻¹ [2038 ]

H₂O: (ice Ih, 0 K) 14.6 kJ ˣ mol⁻¹ [2038]

H₂O: (gas, 0 K) 55.44 kJ ˣ mol⁻¹ [8], 4634.32 cm ⁻¹

HDO: (gas, 0 K) 48.24 kJ ˣ mol⁻¹ [8]

D₂O: (gas, 0 K) 40.54 kJ ˣ mol⁻¹ [8]

18.18.015

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Footnotes

^aVienna Standard Mean Ocean Water. It is impossible (or highly expensive) to prepare isotopically-pure H₂¹⁶O, as there is always some isotopologues present, and it would be readily contaminated. So no properties of this material have been reported. Water from different sources has slight differences in physical properties due to differences in their isotopic composition. The Vienna Standard Mean Ocean Water (VSMOW, now VSMOW2) is pure salt-free water used as a standard water material for determining the physical properties of water. Originally, it was made by mixing distilled ocean waters. It contained 99.984 426 atom % ¹H, 0.015 574 atom % ²H (D), 1.85 x 10⁻¹⁵atom % ³H (T; equivalent to about one disintegration min⁻¹ mol⁻¹ water), 99.76206 atom % ¹⁶O, 0.037 90 atom % ¹⁷O and 0.200 04 atom % ¹⁸O , H₂¹⁶O: H₂¹⁷O: H₂¹⁸O: HD¹⁶O is approximately 100: 0.04: 0.2: 0.02 [IAPWS]. Standard heavy water (D₂O) has the same oxygen isotopic composition but 100% deuterium and molar mass 20.027508 g mol⁻¹ [IAPWS]. With stocks of VSMOW being used up, they have been succeeded as a primary standard by VSMOW2 (~US $10 ml^-1), a standardized artificial pure salt-free water isotopic mixture made to deliver the same isotopic concentrations as VSMOW. Two other standard water preparations exist GISP (Greenland Ice Sheet Precipitation, 0.01246 atom % ²H, 0.03313 atom % ¹⁷O, 0.1522 atom % ¹⁸O) and SLAP (Standard Light Antarctic Precipitation, 0.00905 atom % ²H, 0.02707 atom % ¹⁷O, 0.0929 atom % ¹⁸O). Standard seawater is different (containing many different salts), and its thermodynamic properties are described elsewhere [1452]. The standard for heavy water [4124] contains 100% D₂O with the isotopic composition of oxygen (as D₂¹⁶O, D₂¹⁷O, and D₂¹⁸O) the same as for VSMOW. It should be noted that, although water contains mostly H₂¹⁶O, the concentrations of other isotopologues may well be greater than the solutes of interest in solutions.

The known isotopes of hydrogen and oxygen are ¹H, ²H,³H,⁴H,⁵H, ⁶H, ⁷H, ¹²O, ¹³O, ¹⁴O, ¹⁵O, ¹⁶O, ¹⁷O, ¹⁸O, ¹⁹O, ²⁰O, ²¹O, ²²O, ²³O, ²⁴O, but only ¹H, ²H, ¹⁶O, ¹⁷O, ¹⁸O are stable, the rest being radioactive. Therefore, there are nine stable isotopologues and (theoretically) 355 possible radioactive isotopologues. . If the ortho-/para- magnetic spin state of hydrogen and deuterium are taken into account, the water molecule has 15 different stable forms. [Back]

^b Natural isotopic mixture (VSMOW)^a [IAPWS]. The density of natural water may change by up to 20 g ˣ m⁻³ between distillation fractions or on electrolysis; in both cases, the HD¹⁸O (or D₂¹⁸O at higher HD¹⁸O concentrations) preferentially remaining behind. Freshwater contains less deuterium than ocean water. [Back]

^c1The boiling point of water used to be defined as 100 °C (212 °F) under standard atmospheric pressure (101.325 kPa), but we now use the International Temperature Scale ( ITS-90) where the boiling point is about 99.9743 °C for VSMOW ^a. The boiling point and critical point on the thermodynamic temperature scale have been estimated at 99.9839 °C and 647.113 K, respectively [469 ]. [Back]

^c2The melting point of water (cold hot) used to be defined as 0 °C (32°F) under standard atmospheric pressure (101.325 kPa), but we now use the International Temperature Scale ( ITS-90). 0 °C is now defined as 273.15 K but does not exactly equal the melting point of water, 273.152 519 K ( IAPWS ). Air-saturated water gives a melting point closer to 0 °C. The freezing point of water (hotcold) is ill-defined as water usually freezes a few degrees below 0 °C, and the actual temperature is not reproducible. [Back]

Phase diagram of water (H2O) showing the triple point

^d The precisely reproducible triple point temperature (T.Pt.) was used (employing Vienna Standard Mean Ocean Water ^a) to define the kelvin temperature scale (ITS-90; T.Pt. = 273.16 K exactly and the kelvin degree was 1/273.16 of the thermodynamic temperature of the triple point of VSMOW water). The Celsius scale was defined using the T.Pt. = 0.01 °C with 1 °C made identical in size to 1 K. The triple point is the temperature and pressure at which three phases (here liquid water, hexagonal ice, and water vapor) coexist at equilibrium and transform phase with suitable but tiny changes in temperature or pressure. Also shown, as the dashed line, is the vapor pressure of supercooled liquid water [1729].

Since 2019, the kelvin is defined in terms of the Boltzmann constant, the second, the meter, and the kilogram. [934]

1 K = 0.086 173 332 621 4518 meV = 0.695 034 8004 cm¹ ( ≡ 8.314 4626 J ˣ mol⁻¹). [Back]

^e1 The gram was once defined as exactly the mass of one cubic centimeter of water at 4 °C. [Back]

^e2 The calorie (small calorie; obsolete unit) was defined as the amount of energy needed to raise the temperature of one gram of water one degree Celsius from 19.5-20.5 °C (≈ 4.182 J) and at one atmosphere pressure. [Back]

^f Tritium. Tritium is naturally formed by interactions between cosmic rays (for example, neutrons) and the atmosphere (for example, ), falling to earth as rain (extremely dilute HTO) and having a permanent inventory on Earth of 3.5 kg where its formation (~0.54 g ˣ day⁻¹) equals its radioactive decay [4116]. Tritium (T, ³H, consisting of one proton and two neutrons) has a short half-life of only ~4500 days (12.32 yr) and decays by β-decay (and anti-neutrino, −ν_e, 3.56 ˣ 10¹⁴ Bq ˣ g⁻¹; 9,622 Ci ˣ g⁻¹) to ³He,

+ 18.6 keV

Liquid T₂O is corrosive and undergoes self-radiolysis (≈ 2.1 ˣ 10¹⁵ decays ˣ s⁻¹ ˣ mol⁻¹ T₂O, i.e., ≈ 2.1 P Bq ˣ mol⁻¹ T₂O). The limit for human acceptability of water containing tritium is 10,000 Bq ˣ L⁻¹ (WHO; less than 1 in 10¹³ molecules). The radiative doses received from natural tritium contribute less than a thousandth of the natural background radiation and has no health effects. The biological half-life inside the human body is about a week. The β particles (5.7 keV) travel only about 6 μm in water, but the anti-neutrinos (12.9 keV) escape. The actual atom % of radioactive ³H in water varies between about zero, at the bottom of the oceans, to about 10⁻¹⁴ in atmospheric vapor; with a natural abundance of about 5 ˣ 10⁻¹⁵ % HTO (≈ 2 fM, 25 °C), 6 ˣ 10⁻³² % T₂O [2094]. No other radioactive isotopes (for example, ¹⁵O or ¹⁴O, half-lives 122 s and 71 s respectively) are found naturally in water molecules.

There were peaks in the atmospheric tritium during the later 1950s and early 1960s due to atmospheric nuclear testing releasing 780 kg of tritium. The atmospheric levels are now effectively down to background levels, with the majority of the remaining tritium (~10 kg) spread in the oceans as super-heavy water, HTO. [Back]

^g The possible errors are greater than the last significant figures. [Back]

^h The conductivity (that is, 1/resistance) value is made up by the addition of the limiting ionic conductivities (infinite dilution) of 349.19 S ˣ cm² ˣ mol⁻¹and 199.24 S ˣ cm² ˣ mol⁻¹ for H⁺ and OH⁻ respectively (25 °C), giving a total conductivity, which at pH=7 gives 548.43 ˣ 10⁻⁷ ˣ 10⁻³ S ˣ cm⁻¹ ≈ 0.055 01 μS ˣ cm⁻¹[737]. This corresponds to CO₂-free but not degassed water [711]. The increased conductivity of degassing may be due to the removal of the nonpolar gas (O₂, N₂) structuring effects or increased bicarbonate formation [3450 ]. The conductivities of the D⁺ and OD⁻ ions from D₂O are about 70% and 50% of these values respectively (whether these ratios of 1/√2 and ½ respectively are coincidence or due to the difference in atomic mass and conductivity pathways remains to be determined). [Back]

^j Calculated from ΔG° = -RTLn(K_w) where K_w is from above. This calculation assumes that the standard state of the solvent water is its mole fraction (= 1.0). Alternatively, the values may be calculated from ΔG° = Log_e(10) ˣ RT(pK_w + 2Log₁₀([H₂O]), where [H₂O] is the molar concentration of H₂O or D₂O, where the standard state of the solvent water is taken as 1.0 M. This gives values of 99.78 kJ ˣ mol⁻¹ and 104.76 kJ ˣ mol⁻¹ for H₂O and D₂O respectively. [Back]

^k ${(P+a{n/V}^2)(V-nb)=nRT$ for n moles, with P (pressure), V (volume), R (gas constant), and T (temperature) and 'a' and 'b' are the empirical vdW constants allowing for non-ideal behavior; 'a' allowing for weak attractive interactions and 'b' arising from the finite volumes of the molecules. [Back]

^l Defined as the energy to take a zero kinetic energy gas-phase electron to the bottom of the conduction band of the condensed phase as a delocalized or quasi-free electron [563]. [Back]

^m Molar masses vary according to their source due to isotopic fractionation during phase and chemical changes [2022]; the data does not sum to exactly 100% due to rounding errors ^a. If calculating masses from sums of particles, allowance for the mass-energy conversion is necessary. Some data from spectra.tsu.ru/partfun/. [Back]

ⁿ The coefficient (α) is given by the Hertz–Knudsen equation

where A is the area (m²), N is the number of molecules, t is the time (s), P is water vapor pressure (Pa) (molecules going onto the surface), or the difference in the vapor pressure of the material and the actual vapor pressure present (molecules leaving the surface), M is the molar mass of water (kg mol⁻¹), R is the gas constant (J mol⁻¹ K⁻¹), and T is the temperature (K). For evaporation/sublimation processes, the key factor is the saturation vapor pressure which controls the maximum rate possible (α = 1); ≈ 2 fm day⁻¹ at 100 K, P = ≈ 10 fPa; ≈ 2 pm hr⁻¹ at 120 K, P = ≈ 0.25 nPa; ≈ 1 mm s⁻¹ at 0 °C, P = ≈ 600 Pa. [Back]

The axes for the water molecule, showing the planes of symmetry (xz and yz) and the two-fold axis of rotation (C2, z-axis)

^x The x-direction lies in the plane of the water molecule with the origin on the oxygen and orthogonal to the H-O-H angle (that is, parallel to the longest dimension of the molecule). [Back]

^y The y-direction lies orthogonal to the plane of the water molecule with the origin on the oxygen. [Back]

^z The z-direction lies in the plane of the water molecule with the origin on the oxygen and bisecting the H-O-H angle. [Back]

The figure right also shows the planes of symmetry (xz and yz) and the two-fold axis of rotation (C₂, z-axis).

The quadrupole moments are centered on the oxygen atom ( q_xx= Σ_i c_ix_i² where c = charge, x = distance in x-direction, and the summation is over all (i) charges). Note that calculated quadrupole moments for water vary considerably from model to model. No set of values can be considered 'correct' at presen, except when referring to the particular model and method of calculation. Values calculated with different coordinate systems will be different (see [1731]).

The octupole moments are centered on the center of mass (o_xxz= Σ_i c_ix_i²z_i where c = charge, x and z = distance in x- and z-directions and the summation is over all (i) charges). Note that calculated octupole moments for water vary considerably from model to model and no set of values can be considered 'correct' at the present time, except when referring to the particular model and method of calculation. Values calculated with different coordinate systems will be different (see [1731]). Charge distributions of dipole, quadrupole and octupole moments

^Ω An alternative view of quadrupoles and octupoles [see 1731] involves the linear (Θ₀) and square (Θ₂) quadrupole and the linear (Ω₀) and cubic (Ω₂) octupole; shown in order right after the dipole (μ₀) in which different charges are shown by color. [Back]