Water Properties (including heavy water data)

Ice Data
Spectral data

List of physicochemical data concerning water

Property

Data

Area, surface covered

19.0 Å² molecule^-1 (monolayer [795 ])
9.6 - 10.2 Å²molecule^-1(single molecule; calculated from dimensions)

8.84 Å²molecule^-1(single molecule; basal plane of hexagonal ice)

Atmospheric content

19.66 g kg^-1 (25 °C, 101.325 kPa, relative humidity = 100)

Bond energy, average at 0 K

H₂O, 0.5 (H-O-H O+2H), 458.9 kJ mol bond ^-1

D₂O, 0.5 (D-O-D

O+2D), 466.4 kJ mol bond ^-1

Boiling point, 101.325 kPa

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

D₂O: 101.42 °C [70]

T₂O: 101.51 °C [745 ]

H₂¹⁷O: 100.08 °C [745]

H₂¹⁸O: 100.15 °C [745]

D₂¹⁸O: 101.54 °C [745]

HDO: 100.74 °C [745]

HTO: 100.8 °C [745]

Bulk modulus (=1/κ_T, isothermal elasticity)

H₂O: 2.174 GPa (2.174 nN nm^-2, 25 °C); 8.9 GPa (ice 1h, -20 °C, [717])

D₂O: 2.100 GPa (2.100 nN nm^-2, 25 °C)

CAS registry number

H₂O: 7732-18-5, (H₂O is also known as protium oxide)

D₂O: 7789-20-0 , (D₂O is also known as deuterium oxide)

T₂O: 14940-65-9 , (T₂O is also known as tritium oxide)

Chemical potential (μ)

see Gibbs energy of formation

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

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

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

H₂O (gas): 24460 J mol^-1 MPa^-1 (25 °C)
H₂O (liquid): 18.07 J mol^-1 MPa^-1 (25 °C)
H₂O (solid): 19.73 J mol^-1 MPa^-1 (25 °C)

Cohesive energy density

2.2973 kJ cm^-3 = 2.2973 GPa (= (ΔH_vap-RT)/V_M) (25 °C)

Internal cohesive pressure

168 MPa (25 °C), (= 3.04 kJ mol^-1, 25 °C) [1279]

Compressibility, adiabatic (κ_S)

H₂O: 0.4477 GPa^-1 (25 °C) [620 ], 0.5086 GPa^-1 (0 °C)
Ice Ih: 0.1142 GPa^-1 (0 °C) (IAPWS)

D₂O: 0.4625 GPa^-1 (25 °C) [620]

Compressibility, critical (=P_cV_c/RT_c)

H₂O: 0.2294

D₂O: 0.2277

Compressibility, isothermal (κ_T),

κ_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 (κ_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 (IAPWS)

0.05501 μS cm^-1 (25 °C, [737])^h, 1.2 μS cm^-1 (22 °C, degassed; [711])
Ice Ih: ~0.06 μS cm^-1 (-20 °C) [717] (mainly from surface defects)

Conductivity, thermal

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

D₂O: 0.595 W m^-1 K^-1 (25 °C) [IAPWS]

Conductivity, thermal; maximum

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

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

Critical point

H₂O: 647.096 K,^c1 22.064 MPa, 322 kg m^-3 (IAPWS)^g

D₂O: 643.847 K, 21.671 MPa, 356 kg m^-3 (IAPWS) ^g

T₂O: 641.657 K, 21.385 MPa, 376 kg m^-3[830 ]^g

Critical point, second

H₂O: no generally accepted value, for example, ~217 K, ~340 MPa, ~1130 kg m^-3 [419 ]; ~188 K, ~230 MPa, ~1100 kg m^-3 [432 ]; ~182 K, ~195 MPa [580 ]; 145-175 K, ~200 MPa [999 ]; 223 K, ~50 MPa [1685 ]

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

Cryoscopic constant

1.8597 K kg mol^-1

Density

997.05 kg m^-3(25.0 °C, 101.325 kPa) [67, 112], 997.047 013 kg m^-3 (25 °C, 0.1 MPa [IAPWS] from formula)

H₂O

2260 kg m^-3(liquid, ~1500 K, 57 GPa) [1218 ]

H₂¹⁸O

1110.64 kg m^-3 (20.0 °C) [745]

HDO

1050.7 kg m^-3 (25.0 °C) [1857 ]

D₂O

1104.36 kg m^-3 (25.0 °C) [620]

D₂¹⁸O

1216.22 kg m^-3 (20.0 °C) [745]

Density of ice at melting point^a

H₂O: 916.72 kg m^-3 (0 °C, 101.325 kPa) (IAPWS)

D₂O: 1017.5 kg m^-3 (3.82 °C)

Density of liquid water at melting point [70]

H₂O: 999.84 kg m^-3 (0 °C, 101.325 kPa)

D₂O: 1105.46 kg m^-3 (3.813 °C)

Density of gas at boiling point

H₂O: 0.5976 kg m^-3(100 °C, 101.325 kPa) [540]

Density maximum (and molar volume) at temperature of maximum density [67, 112]

999.97495 kg m^-3e

3.984 °C

H₂O

999.972 kg m^-3, 29.91 Å³ mol^-1

999.975 kg m^-3 ( IAPWS formula)

3.984 °C

3.978 °C ( IAPWS)

D₂O

1105.3 kg m^-3, 30.07 Å³ mol^-1

11.185 °C

T₂O

1215.01 kg m^-3, 30.10 Å³ mol^-1

13.403 °C

H₂¹⁸O

1112.49 kg m^-3, 29.87 Å³ mol^-1

4.211 °C

D₂¹⁸O

1216.88 kg m^-3, 30.06 Å³ mol^-1

11.438 °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: 9.55 x 10^-12s (20 °C) [8]

H₂O Ice Ih: ~2 x 10^-5s (0 °C)

D₂O: 12.3 x 10^-12s (20 °C) [8]

Diffusion coefficient

H₂O: 0.2299 Å² ps^-1 (25 °C) [1933 ], 0.0187 Å² ps^-1 (-31 °C) [62];
6 x 10^-8Å² ps^-1 (ice 1h, -20 °C) [717 ]
~10^-8Å² ps^-1 (amorphous water, ~160 K) [334]

D₂O: 0.2109 Å² ps^-1 (25 °C) [8]

H₂¹⁸O: 0.266 Å² ps^-1 [745]

HDO: 0.234 Å² ps^-1 [745]

HTO: 0.244 Å² ps^-1 [745]

Diffusivity, thermal
()

H₂O: 14.6 Å² ps^-1 (25 °C)

Ice Ih: 84.3 Å² ps^-1 (0 °C)

D₂O: 12.7 Å² ps^-1 (25 °C)

Dipole moment (average), μ ^z

2.95±0.2 D (liquid, 27 °C) [129], 1.85498 D (gas, 6.1875×10^-30 C m) [IAPWS],
3.09 D (ice) [238]

1.8517 D (HDO gas, [IAPWS])

Displacement, root mean square

~0.07 mm s^-1 [1577a]

Ebullioscopic constant

0.5129 K kg mol^-1

Electron affinity [563 ]

-16 kJ mol^-1 (-0.17 eV) (25 °C)^l
HOMO-LUMO gap, 659 kJ mol^-1 (6.83 eV) (25 °C)

Elemental composition ^a

Hydrogen (all isotopes), 11.1903 % w/w

Oxygen (all isotopes), 88.8097 % w/w

Energy, internal (U) [540 ]

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

Enthalpy (H = U + PV) [67]

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

Enthalpy of formation, ΔH_f, [808]

H₂O: -285.85 kJ mol^-1 (25 °C)

D₂O: -294.6 kJ mol^-1 (25 °C)

Enthalpy of vaporization (liquid)

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

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

Enthalpy of fusion

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

H₂¹⁸O: 6.029 kJ mol^-1 (0.31 °C) [1710]

D₂¹⁶O: 6.315 kJ mol^-1 (3.82 °C) [1710]

HD¹⁶O: 6.227 kJ mol^-1 (2.04 °C) [1710]

Enthalpy of sublimation (ice Ih)

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

Entropy (S)

63.45 J mol^-1 K^-1 (Absolute entropy at triple point) [869 ]
6.6177 J mol^-1 K^-1 (25 °C) [67]
Ice Ih: -21.99 J mol^-1 K^-1 (0 °C) (IAPWS)

Ice Ih: 3.408 J mol^-1 K^-1 (0 K) [1832 ] ~ RLn(3/2)
gas: 132.5 J mol^-1 K^-1 (100 °C, 101.325 kPa) [540]

Entropy, molar

see Chemical potential, temperature coefficient (dμ/dT)

Entropy of fusion [8]

22.00 J mol^-1 K^-1 (0 °C)

Entropy of vaporization [8]

108.951 J mol^-1 K^-1 (100 °C)

Expansion coefficient (α),

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

H₂O: 0.000000 °C^-1(3.984 °C), 0.000253 °C^-1 (25 °C) [68]
Ice Ih: 0.0001598 °C^-1 (0 °C, 101.325 kPa) (IAPWS); 0.000053 °C^-1 (-20 °C) [717]

D₂O: 0.0001722 °C^-1(25 °C) [620]

Fragile to strong liquid transition

~220 K [1200]

Gas constant (R⁹⁵)

461.51805 J kg^-1 K^-1 (IAPWS)

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

-82.157 J mol^-1 (25 °C, 101.325 kPa) [540]
Ice Ih: 1.826 J mol^-1 (0 °C, 101.325 kPa) (IAPWS)
gas: -1239 J mol^-1 (100 °C, 101.325 kPa) [540]

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

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

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

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

Glass transition temperature

136 K (this has been subject to dispute [312])

Heat capacity ratio (γ=C_P/C_V)

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

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

-83.989 J mol^-1 (25 °C, 101.325 kPa)
Ice Ih: -0.166 J mol^-1 (0 °C, 101.325 kPa) (IAPWS)
gas: -4293 J mol^-1 (100 °C, 101.325 kPa)

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

Ionic dissociation constant,
[H⁺][OH^-]/[H₂O] (25 °C) [808]

H₂O: 1.821 x 10^-16 mol l^-1(25 °C) [808]

H₂O Ice Ih: 3.8 x 10^-22 mol l^-1 (-10 °C) [1831 ]

D₂O: 3.54 x 10^-17 mol l^-1(25 °C) [808]

D₂O: Ice Ih: 1.9 x 10^-23 mol l^-1(-10 °C) [1831]

T₂O: ~1.1 x 10^-17 mol l^-1(25 °C) [808]

Ionization in liquid water, ΔG (25 °C)

2H₂O H₃O⁺ + OH^- 79.907 kJ mol^-1 ^j

2D₂O

D ₃O⁺ + OD^- 84.88 kJ mol^-1 ^j

Ionization potential

H₂O: gas; 1216 kJ mol^-1 (12.61 eV) [381a ]
H₂O: liquid; 1018 kJ mol^-1 (10.56 eV) [381a]
H₂O: ice; 1061 kJ mol^-1 (11.00 eV) [381a]

D₂O: 1219 kJ mol^-1 (12.64 eV) [381b]

Ionization rate (25 °C)

H₂O H⁺ + OH^- 2.59x10^-5 L mol^-1 s^-1H⁺ + OH^- H₂O 1.43x10¹¹ L² mol^-2 s^-1

Limits of stability for liquid water

Lowest temperature, -22 °C at 207.5 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 mol^-1(25 °C), -1.63x10^-10 m³ 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

H₂O: 1.634 cm³ mol ^-1

D₂O: 1.567 cm³ mol ^-1

Melting point, 101.325 kPa [70, 88]

H₂O: 0.00 °C ^c2, 273.152519 K (IAPWS)

D₂O: 3.82 °C

T₂O: 4.49 °C

H₂¹⁸O: 273.43 K [829 ]

Melting point, pressure coefficient

-74.293 mK MPa^-1(0 °C) [1385]

Molality ^b

H₂O: 55.508472 mol kg ^-1

D₂O: 49.931324 mol kg ^-1

Molar concentration ^b

H₂O: 55.345 mol L^-1(25 °C)

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

D₂O: 55.142 mol L^-1(25 °C)

Molar isotopic composition ^a, ^m

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

H₂¹⁶O

99.7317 %

18.01056469 g mol^-1

H₂¹⁷O

0.0372 %

19.01478156 g mol^-1

H₂¹⁸O

0.199983 %

20.0148105 g mol^-1

HD¹⁶O

0.031069 %

19.01684143 g mol^-1

HD¹⁷O

0.0000116 %

20.02105831 g mol^-1

HD¹⁸O

0.0000623 %

21.0210872 g mol^-1

D₂¹⁶O

0.0000026 %

20.02311818 g mol^-1

HT¹⁶O

variable trace ^f

20.01878892 g mol^-1

T₂¹⁶O

0 %

22.02701316 g mol^-1

Molar mass ^b

H₂O: 18.015268 g mol^-1

D₂O: 20.027508 g mol^-1

Molar volume (gas, STP)

0.022199 m³ mol^-1 (0 °C, 101.325 kPa)

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]

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]

O-H bond dissociation energy, 492.2148 kJ mol^-1 [350]

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

D-O-D bond angle (liquid), 106° [91]

Molecular mass

H₂O:^b 2.9915051 x 10^-23 g molecule^-1

H₂¹⁶O: 2.9907243 x 10^-23 g molecule^-1

D₂¹⁶O: 3.3249166 x 10^-23 g molecule^-1

Moment of inertia (axes through centers of mass)

H₂O: 1.0220 x 10^-40 g cm² ^x; 2.9376 x 10^-40 g cm² ^y; 1.9187 x 10^-40 g cm² ^z [8]

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

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

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 Å² ^xxz; -0.554 D Å² ^yyz; -1.981 D Å² ^zzz

Octupole moment, (alternative)

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

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

H₂O: 2.34

H₂¹⁸O: 2.28

D₂O: 2.29

Other systematic names for water

Oxidane (IUPAC)

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

0.3925

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 L^-1; [IAPWS])

Piezoscopic constant (= R/V_m)

H₂O: 0.4602 MPa K^-1 (25 °C)

D₂O: 0.4585 MPa K^-1(25 °C)

T₂O: 0.4580 MPa K^-1 (25 °C)

pK_a

H₂O: 15.738 (25 °C) [IAPWS]

D₂O: 16.610 (25 °C) (based on [70])

pK_w

H₂O: 13.995 (25 °C)[IAPWS]

D₂O: 14.87 (25 °C) [70]

Polarity/dipolarity, π [666]

1.09

Polarizability, ()

1.62x10^-40 F m²

Polarizability volume ,

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

Prandtl Number
(= kinematic viscosity / thermal diffusivity)

H₂O: 6.12 (25 °C)

D₂O: 7.81 (25 °C)

Quadrupole moment, Q, 25 °C

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

Quadrupole moment (alternative)

linear (Θ₀) 0.28 D Å; square (Θ₂) 2.13 D 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: 1.33286 (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:1.32828 (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

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

Shear modulus (adiabatic elasticity)

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

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

Specific heat capacity,

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

H₂O: 75.338 J mol^-1 K^-1; 4.1819 kJ kg^-1 K^-1, 4.1696 MJ m^-3 K^-1 (25 °C, 101.325 kPa, calculated from [1154 ]), 4.181 446 18 kJ kg^-1 K^-1 (25 °C, 0.1 MPa [IAPWS] from formula)
H₂O: 89.22 J mol^-1 K^-1 (240 K) [906]
Ice Ih: 37.77 J mol^-1 K^-1 (0 °C) (IAPWS), 22.10 J mol^-1 K^-1 (150 K) [906]
gas: 37.47 J mol^-1 K^-1 (100 °C, 101.325 kPa) [540]

D₂O: 84.67 J mol^-1 K^-1 ; 4.228 kJ kg^-1 K^-1, 4.669 MJ m^-3 K^-1 (25 °C, calculated from [620])

Specific heat capacity minimum, C_P,min

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

D₂O: 83.21 J mol^-1 K^-1 at 121 °C, calculated from [1453]

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

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

D₂O: 84.42 J mol^-1 K^-1 (25 °C) [620]

Speed of sound

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

Ice Ih: 3837.9 m s^-1 (0 °C) [1812 ]
gas: 472.2 m s^-1 (100 °C, 101.325 kPa) [540]

D₂O: 1399.2 m s^-1 (25 °C)

Speed of sound, maximum

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

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

Standard state of water

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

Surface entropy (= -dγ/dT)

H₂O: 0.1542 mJ m^-2 K^-1 (25 °C) (calculated from IAPWS)

Surface enthalpy (surface energy)

H₂O: 0.1179 J m^-2 (25 °C) (= γ -T dγ/dT; calculated from IAPWS)

Surface tension (change with pressure)

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

Surface tension (

)

H₂O: 0.07198 N m^-1(25 °C; 0.07198 J m^-2) [IAPWS]

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

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

Triple point

H₂O: 0.01 °C exactly (273.16 K exactly) by definition^d for VSMOW^a, 611.657 Pa, 0.99978 g cm^-3 [536]
Isotopically pure ¹H₂¹⁶O: 0.0087 °C [565 ]

D₂O: 3.80 °C, 660.096 Pa, 1.1056 g cm^-3[IAPWS]

H₂¹⁷O: 0.21 °C [745]

H₂¹⁸O: 0.31 °C [717]

D₂¹⁶O: 3.82 °C [1710]

D₂¹⁸O: 4.13 °C [745]

HD¹⁶O: 2.04 °C [1710]

HTO: 2.4 °C [745]

T₂O: 4.49 °C [716 ], 662.9 Pa [830]

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

~640 m s^-1 [1577a]

Viscosity, dynamic

H₂O: 0.8909 mPa s (25 °C, 101.325 kPa) [IAPWS], 0.889 996 774 mPa s (25 °C, 0.1 MPa [IAPWS] from formula); 1.0016 mPa s (20 °C, 101.325 kPa) [745]
gas: 0.0123 mPa s (100 °C, 101.325 kPa) [540]

D₂O: 1.095 mPa s (25 °C) [IAPWS]; 1.2467 mPa s (20 °C) [745]

H₂¹⁸O: 1.0564 mPa s (20 °C) [745]

D₂¹⁸O: 1.3050 mPa s (20 °C) [745]

HDO: 1.1248 mPa s (20 °C) [745]

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

Viscosity, kinematic

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

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

Viscosity, bulk (volume viscosity)

2.47 mPa s (25 °C) [1703]

Viscosity, temperature coefficient

0.0199 mPa s K ^-1 (25 °C) [304]

Van der Waals gas constants [70] ^k

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

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

H₂O: 18.0182 cm³ (0 °C) 18.0685 cm³ (25 °C) [1006 ]; 19.66 cm³(ice Ih, 0 °C); 0.030143 m³(gas, 100 °C)

H₂O: 50.6 Å³ 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: 18.1331 cm³ (25 °C) [1006]

D₂¹⁷O: 18.1297 cm³ (25 °C) [1006]

D₂¹⁸O: 18.1263 cm³ (25 °C) [1006]

T₂O: 18.1549 cm³ (25 °C) [1006]

Volume, intrinsic H₂O

11.01 Å³

Volume, molecular H₂O at 101.325 kPa

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

Volume, van der Waals

14.6 Å³ molecule^-1 (liquid)

Zero point energy (calculated from gaseous vibrations) [8]

H₂O: 55.44 kJ mol^-1

HDO: 48.24 kJ mol^-1

D₂O: 40.54 kJ mol^-1

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Footnotes

^aThe Vienna Standard Mean Ocean Water (VSMOW) is pure salt-free water used as a standard material and containing 99.984426 atom % ¹H, 0.015574 atom % ²H (D), 18.5 x 10^-16atom % ³H (T; equivalent to about 2 d.p.m. mol^-1), 99.76206 atom % ¹⁶O, 0.03790 atom % ¹⁷O and 0.20004 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 salt) is described elsewhere [1452].

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) 537 possible radioactive isotopologues. [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]

^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 (coldhot) 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, 273.152519 K (IAPWS). Note that the freezing point of water (hotcold) is ill-defined as water usually freezes a few degrees below 0 °C, 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.) 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]

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

^f Tritium (T, ³H) has a half-life of 4500±8 days and decays by β-decay (and anti-neutrino) to ³He ().

Liquid T₂O undergoes self-radiolysis (~4.4 x 10¹⁵ decays s^-1 mol^-1 T₂O, i.e. ~4.4 PBq 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; typically about 2 x 10^-16 in liquid water. It is naturally formed by interactions between cosmic rays (for example, neutrons) and the atmosphere (for example, ), 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. [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 cm² mol^-1and 199.24 for H⁺ and OH^- respectively (25 °C), giving a total conductivity, which at pH=7 gives 548.43 x10^-7x10^-3S cm^-1 = 0.05501 μS 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(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)xRT(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 mol^-1 and 104.76 kJ mol^-1 for H₂O and D₂O respectively. [Back]

^k ${(P+a{n/V}^2)(V-nb)=nRT$ for n moles. [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; the data does not sum to exactly 100% due to rounding errors ^a. [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 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 (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 moments, from left to right: a linear
dipole; a linear quadrupole; a square quadrupole; a linear octupole;
and a cubic octupole, in which positive charge is blue and negative
charge is red.

^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]