## Abstract

The thermochemical properties (osmotic coefficient, enthalpy and heat capacity) of seawater from S=0 to 120 and 0 to 200°C have been fit to the Pitzer equations. The osmotic coefficient (φ), apparent molal heat capacity (^{φ}Cp) and relative enthalpy (^{φ}L) have been fit to equations of the form φ_{SS}-1=(1/m){-A_{φ}I ^{1.5}/(1+1.2I^{0.5})+m(B_{SS}^{φ}+mC _{SS}^{φ})}^{φ}Cp_{SS}-C̄p _{ss}^{0}=A_{J}{I/(1.2m)}ln(1+1.2I^{0.5}) +2RTm(B_{SS}^{J}+mC_{SS}^{J}) ^{φ}L_{SS}=(A_{H}I/1.2m)ln(1+1.2I ^{0.5})-2RTm(B_{SS}^{L}+mC_{SS} ^{L})where I is the ionic strength, m is the molality of sea salt (m=∑m_{i}, i is an ion); A_{X} (X=φ, J and H) is the Debye-Hückel slope, and C̄p_{ss}^{0} is the apparent molal heat capacity of sea salt in water. The Pitzer parameters B _{SS}^{X} and C_{SS}^{X} for sea salt have been fit to functions of temperature in the form Y_{SS}^{X}= ∑a_{ij}(T-T_{R})^{i}where a_{ij} are adjustable parameters, Y_{SS}^{X} is the Pitzer coefficient, T is the temperature in K, and T_{R}=273.15 K). The standard deviations of the seawater fits were 0.0006 J g^{-1} K^{-1} for the heat capacity from 0 to 40°C and 0.0038 J g^{-1} K^{-1} from 0 to 200°C. The extrapolated values of C̄p_{ss}^{0} from 0 to 200°C were in reasonable agreement with the values determined from the major sea salts. The combined c_{p} data have been fit to equations that are consistent with the theoretical values of C̄p_{ss} ^{0}. By appropriate integration of ^{φ}Cp_{SS}, the apparent molal enthalpy at 298 K and osmotic coefficients at 273 K, equations were determined for all the thermochemical properties as a function of ionic strength and temperature. The thermochemical properties determined in this manner are in good agreement with direct measurements at different salinities and temperatures. The equations can be used to determine all the thermochemical properties of seawater from 0 to 200°C and I=0 to 2.4 (S=120).

Original language | English (US) |
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Pages (from-to) | 81-99 |

Number of pages | 19 |

Journal | Marine Chemistry |

Volume | 94 |

Issue number | 1-4 |

DOIs | |

State | Published - Mar 1 2005 |

## Keywords

- Apparent molal enthalpies
- Apparent molal heat capacity
- Free energies
- Osmotic coefficients
- Pitzer equations
- Sea salts
- Seawater

## ASJC Scopus subject areas

- Oceanography
- Chemistry(all)
- Environmental Chemistry
- Water Science and Technology