The Molecular Basis for the Heat Capacity and Thermal Expansion of Natural Waters

The high heat capacity of seawater has been cited as why 93% of the heat trapped by anthropogenic greenhouse gases is absorbed by the ocean. Specific heats (C P ) are closely tied to molecular weight. The mean molecular weight of pure water over the range 0–40 °C is 86.1–80.7 and 89.4–84.5 for seawater. Warming of water increases the kinetic energy of the molecules and induces breaking of hydrogen bonds (8.364 kJ/mol); both effects increase the volume of the fluid. Warming pure water from 0–10 °C increases the single H 2 O molecular form by 1.64%, accounting for 36.3% of the energy consumed. The specific heat of pure water is thus attributable (63.7%) to increasing the kinetic energy of the water, and (36.3%) to the energy required to break hydrogen bonds. For seawater, 34.7% of the energy goes to breaking hydrogen bonds while the rest (65.3%) is attributable to increasing the kinetic energy of the molecules.