Chemistry · Ch 9 — Hydrogen
Physical Properties of Water
9.6.1
Physical Properties of Water
Physical Properties
Pure water is a colourless and tasteless liquid. Its physical constants, alongside those of heavy water (), are compared below.
Table 9.3 — Physical Properties of H₂O and D₂O
| Property | H₂O | D₂O |
|---|---|---|
| Molecular mass (g mol⁻¹) | 18.0151 | 20.0276 |
| Melting point (K) | 273.0 | 276.8 |
| Boiling point (K) | 373.0 | 374.4 |
| Enthalpy of formation (kJ mol⁻¹) | −285.9 | −294.6 |
| Enthalpy of vaporisation, 373 K (kJ mol⁻¹) | 40.66 | 41.61 |
| Enthalpy of fusion (kJ mol⁻¹) | 6.01 | — |
| Temperature of max. density (K) | 276.98 | 284.2 |
| Density, 298 K (g cm⁻³) | 1.0000 | 1.1059 |
| Viscosity (centipoise) | 0.8903 | 1.107 |
| Dielectric constant (C² N⁻¹ m⁻²) | 78.39 | 78.06 |
| Electrical conductivity, 293 K (Ω⁻¹ cm⁻¹) | — |
Why water behaves so unusually: water's condensed-phase behaviour (liquid and solid) is dominated by extensive hydrogen bonding between molecules. This is what gives it its unusually high freezing point, boiling point, heat of vaporisation and heat of fusion compared with the heavier hydrides and . Water also has an unusually high specific heat, thermal conductivity, surface tension, dipole moment and dielectric constant relative to other common liquids.
These properties are what make water so important biologically: …
Table 9.3Physical Properties of H2O and D2O
| Property | H2O | D2O |
|---|---|---|
| Molecular mass (g mol^-1) | 18.0151 | 20.0276 |
| Melting point/K | 273.0 | 276.8 |
| Boiling point/K | 373.0 | 374.4 |
| Enthalpy of formation/kJ mol^-1 | -285.9 | -294.6 |
| Enthalpy of vaporisation (373K)/kJ mol^-1 | 40.66 | 41.61 |
| Enthalpy of fusion/kJ mol^-1 | 6.01 | - |
| Temp of max. density/K | 276.98 | 284.2 |
| Density (298K)/g cm^-3 | 1.0000 | 1.1059 |
| Viscosity/centipoise | 0.8903 | 1.107 |