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Short data list for liquid water

Water Properties (including isotopologues)

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List of physicochemical data concerning water

Property

Data

Absorption coefficient , max.( λ > 180 nm)

                                    min.

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

0.000 0442 cm-1 (at 417.5.5 nm wavelength) [130]

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 'goes to' arrow ·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 'goes to' arrow ·O·+2D·), 466.4 kJ ˣ mol ˣ bond -1

HDO, (H-O-D 'goes to' arrow H· + ·O-D), 493.336 kJ ˣ mol-1 [350]

Boiling point, 101.325 kPa

H2O: 100.0 °C c1 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]
D216O: 101.40 °C [745]
D218O: 101.54 °C [745]
HTO: 100.8 °C [745]
T2O: 101.51 °C [745 ]

Bulk modulus (=1/ κT , isothermal elasticity)

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 (= ( ΔHvap - R T)/ VM) (25 °C)

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

Internal cohesive pressure

168 MPa (25 °C), Change in internal energy with volume at constant temperature (equivalent to 3.04 kJ ˣ mol-1, 25 °C) [1279]

Color approximate color through several meters of waterH2O: very slight blue color
approximate color through several meters of heavy waterD2O: colorless

Combining volumes

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

Compressibility, adiabatic S), also called isentropic compressibility

H2O: 0.4477 GPa -1 (25 °C) [620], 0.5086 GPa -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 (= Pc Vc / R Tc)

H2O: 0.2294

D2O: 0.2277

Compressibility, isothermalT),

κT = -(1/V)(δV/δP)T = <(ΔV)2>/(kBTV) [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, isothermalT), 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 , 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+ : λH = 349.19 S ˣ cm2 ˣ mol-1 (25 °C, [737])

OH- : λOH = 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 (Tc, Pc, ρc, Vc)

H2O: 647.096 K, c1 22.064 MPa , 322 kg m-3, 3.1056 cm3 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

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].

D2O: ~-78 °C, ~230 MPa , ~1220 kg m-3 [450 ]; ~-86 °C, ~211 MPa [580]

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)

a

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

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)

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

a

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

11.185 °C

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 10-12 s (25 °C) [2414]

H2O ice Ih: ~2 ˣ 10-5 s (0 °C)

D2O: 12.3 ˣ 10-12 s (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];
6 x 10-8 Å2 ˣ ps-1 (ice Ih, -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)

H217O: 0.104 rad2 ˣ ps-1 (25 °C) [2112]

D217O: 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
                          =thermal conductivity/(density x specific heat)

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: 1.85498 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 'goes to' arrow H3O+ + OH-   79.907 kJ ˣ mol-1 j

H-O-H 'goes to' arrow H· + ·O-H see bond energies

2D2O 'goes to' arrow D 3O+ + OD-   84.88 kJ ˣ mol-1 j

Dissociation rate (25 °C)

H2O 'goes to' arrow H+ + OH-           2.59 ˣ 10-5 L ˣ mol-1 ˣ s-1
H+ + OH- 'goes to' arrow H2O           1.43 ˣ 1011 L2 ˣ mol-2 ˣ s-1

Dissociation thermodynamics (25 °C)

H2O (liq)equilibrium arrows H+(aq) + OH- (aq) [1938]

ΔU° = 59.5 kJ ˣ mol-1

ΔV° = 22.13 cm3 mol-1

ΔH° = 55.8 kJ ˣ mol-1

ΔG° = 79.9 kJ ˣ mol-1

ΔS° = -80.8 J K-1 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]

-16 kJ ˣ mol-1 (-0.17 eV) (25 °C) l
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, ΔHf,   

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 (ΔHvap, liquid)  

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 (3.82 °C), 41.521 kJ ˣ mol-1 (101.42 °C), calculated from [1453]

Enthalpy 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]

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]
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
gas: 132.5 J ˣ mol-1 ˣ K-1 (100 °C, 101.325 kPa) [540]

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 n

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

Expansion coefficient (α),

αP = (1/V)(δV/δT)P = <(ΔV)(ΔS)>P/(kB2T) [1373b]

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

-0.002963 (-20 °C), +0.0004930 (250 K, 400 MPa) [2089]
ice Ih: 0.0001598 °C-1 (0 °C, 101.325 kPa) ( IAPWS ); 0.000053 °C-1 (-20 °C) [717]

D2O: 0.000 1722 °C-1 (25 °C) [620]

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 (RS) = 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/Vmolecule  ; RT/Vmole   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]
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, ΔGf,
   = 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=CP/CV)

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]

γxxxx = -0.46 D ˣ Å3 , γyyyy = 1.53 D ˣ Å3, γzzzz = -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 (DN), 18.0 [456]; compare CH3CN 14.1; CH3OH, 19.0
Acceptor number (AN), 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

H2O: gas; 1216 kJ ˣ mol-1 (12.61 eV) [381a]; 101,766.3 cm-1 [2571]
H2O: liquid; 1018 kJ ˣ mol-1 (10.56 eV) [381a]
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]

Joule-Thomson coefficient (25 °C)

0.214 K MPa -1 [ IAPWS]

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

Magnetic susceptibility [670 ]

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

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 , 273.152 519 K ( IAPWS)

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

1410 K at 72 GPa [2096]

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

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
Molar masses may be calculated
H 1.007 825 032 07 g ˣ mol-1
D 2.014 101 777 85 g ˣ mol-1
T 3.016 049 2777 g ˣ mol-1
16O 15.994 914 619 56 g ˣ mol-1
17O 16.999 131 50 g ˣ mol-1
18O 17.999 1604 g ˣ mol-1

H216O

99.7317 % (55.21 M, 25 °C)

18.010 564 69 g ˣ mol-1

H217O

0.0372 % (19.51 mM, 25 °C)

19.014 781 56 g ˣ mol-1

H218O

0.199983 % (99.62 mM, 25 °C)

20.014 8105 g ˣ mol-1

HD16O

0.031069 % (16.29 mM, 25 °C)

19.016 841 43 g ˣ mol-1

HD17O

0.0000116 % (5.8 µM, 25 °C)

20.021 058 31 g ˣ mol-1

HD18O

0.0000623 % (29.5 µM, 25 °C)

21.021 0872 g ˣ mol-1

D216O

0.0000026 % (1.3 µM, 25 °C)

20.023 118 18 g ˣ mol-1

D217O ~5 nM, 25 °C; calculated 21.027 335 06 g ˣ mol-1
D218O ~26 nM, 25 °C; calculated 22.027 363 96 g ˣ mol-1

HT16O

variable trace f

20.018 788 92 g ˣ mol-1

T216O 0 % f 22.027 013 16 g ˣ mol-1

Molar mass b

H2O: 18.015265 g mol-1 (compare molar mass of dry air 28.965 46 g ˣ mol-1 [2215])

D2O: 20.027 508 g mol-1

Molar volume (gas, STP)

0.022 199 m3 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])

d2phi by dtheta squared = 432.47 kJ ˣ mol-1 ˣ rad-2

d2phi by dr1 squared = 5,096.32 kJ ˣ mol-1 ˣ Å-2

d2phi by dr1  dr2= -57.116 kJ ˣ mol-1 ˣ Å-2

d2phi by dr1 dtheta= 226.05 kJ ˣ mol-1 ˣ Å-1 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]

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

D2O: deuterium oxide ('heavy water')
T2O: tritium oxide ('superheavy water')
Common 'hoax' name for water
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]
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]
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

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]

pD

D2O: 7.43 (25 °C) (based on [70])

pHD HDO: 7.266 (25 °C)

pH

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

HTO: 7.6 (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/Vm)

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)

pKa and pKb

pKa H2O: (= pKb H2O) = 13.995 (25 °C) [2965]

pKa H3O+: (= pKb OH-) = 0.0 (exactly and invariant of temperature) [2967]
pKa D2O: (= pKb D2O) = 14.869 (25 °C) (based on [70])
pKa D3O+: (= pKb OD-) = 0.0 (exactly and invariant of temperature)

pKw

H2O: 13.995 (25 °C) [IAPWS]

D2O: 14.869 (25 °C) [70]

Polarity/dipolarity, π [666]

1.09

Polarizability , (polarizability  = polarizability volume x 4 x pi x vacuum permittivity))

1.636 ˣ 10-40 F ˣ m2

Polarizability volume , polarizability volume = polarizability/(4 x pi x vacuum permittivity)

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
      (= 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 [2334]

Proton spin-spin relaxation time (25 °C)

T2 = 1.86 ± 0.07 s [2098] ; 3.59 s [2334]

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 'goes to' arrow O2(g) + 4H+ + 4e-          -E° = -1.229 V (25 °C, pH 0)
2H2O + 2e- 'goes to' arrow 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: ηO 1.3091; ηE 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 cm (25 °C, pH 6.9976, ultrapure water [737]) h , 0.8 MΩ 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 ,

CP = (δH/δT)P = T(δS/δT)P = <(ΔS)2>/kB [1373b]

H2O: 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: 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])

Specific heat capacity minimum, CP,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 , Cv = (∂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]

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) Change in surface tension with pressure=change in volume on change in surface area

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

Surface tension (Surface tension =change in free energy per change in surface area at constat temperature and pressure)

         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, γsl); 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, γsg); 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]

Triple point

H2O: 0.01 °C exactly (273.16 K exactly) by definition d for VSMOW a , 611.654 771 007 894 Pa [IAPWS], 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: 3.80 °C, 660.096 Pa , 1.1056 g cm-3 (liquid) [IAPWS], 0.00575 kg ˣ m-3 (gas)
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) [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 , VM,
see also chemical potential, pressure coefficient (dμ/dP)

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

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: 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

11.01 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; hexagonal ice, 9 GPa (disputed) [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]

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Footnotes

a   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 and the Kelvin and Celsius temperature scales (using the triple point of water, 0.01  °C, 273.16 K). It is made by mixing purified ocean waters. It contains 99.984 426 atom % 1H, 0.015 574 atom % 2H (D), 1.85 x 10-15 atom % 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 [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 by VSMOW2 , a standardized artificial pure salt-free water isotopic mixture made to deliver the same isotopic concentrations. 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 (containing many different salts) and its thermodynamic properties are described elsewhere [1452]. 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 9 stable isotopologues and (theoretically) 355 possible radioactive isotopologues. If the ortho-/para- magnetic spin states of hydrogen and deuterium are taken into account, there are 15 different stable forms of the water molecule. [Back]

 

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

 

c1   The 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]

 

c2   The 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. Note that the freezing point of water (hot-->cold) 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 triple point

 

d  The precisely reproducible triple point temperature (T.Pt.) is 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 is 1/273.16 of the thermodynamic temperature of the triple point of VSMOW water). The Celsius scale is 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 will 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]. [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 (T, 3H) has a half-life of 4500±8 days and decays by β-decay (and anti-neutrino) to 3He (Tritium decays by beta and anti-neutrino decay to helium).

Liquid T2O undergoes self-radiolysis (~ 2.1 ˣ 1015 decays ˣ s-1 ˣ mol-1 T2O, i.e. ~2.1 PBq ˣ mol-1 T2O). The β particles (5.7 KeV) travel only about 6 μm in water, but the antineutrinos (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 natural abundance of about 5 ˣ 10-15 % HTO (~2 fM, 25 °C), 6 ˣ 10-32 % T2O [2094]. It is naturally formed by interactions between cosmic rays (for example, neutrons) and the atmosphere (for example, Nitrogen-14 + neutron gives carbon-12 + tritium), falling to earth as rain (HTO). 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 atmospheric tritium during the later 1950s and early 1960s due to atmospheric nuclear testing. The atmospheric levels are now down to background levels. [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 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 on degassing may be due to the removal of the non-polar gas (O2, N2) structuring effects. 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 1/2 respectively are coincidence or due to the difference in atomic mass and conductivity pathways remains to be determined). [Back]

 

j  Calculated from ΔG° = -RTLn(Kw) where Kw 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° = Loge(10) ˣ RT(pKw + 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 quasifree electron [563]. [Back]

 

m   Molar masses vary according to 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. [Back]

 

n  The coefficient (α) is given by the Hertz–Knudsen equation       dN/Adt=alpha x pressure x Avogadro number/sqrt(2 x Pi x molar mass x  gas constant x Temperature)

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 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 ( qxx= Σi cixi2 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 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]).

 

The octupole moments are centered on the center of mass (oxxz= Σi cixi2zi 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]

 

 

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This page was established in 2000 and last updated by Martin Chaplin on 24 September, 2017


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