Molar volume isotope effect water

IE s on some of the other properties of water are shown in Table 5.9. Many properties (like the enthalpies of phase change, triple points, etc.) are closely related to VP and can be interpreted similarly. Molar volume isotope effects are interesting and are discussed in Chapters 12 and 13. In the low temperature liquids... 

Table 13.1). In the solid P(CH4) > P(CD4) but the curves cross below the melting point and the vapor pressure IE for the liquids is inverse (Pd > Ph). For water and methane Tc > Tc, but for water Pc > Pc and for methane Pc < Pc- As always, the primes designate the lighter isotopomer. At LV coexistence pliq(D20) < Pliq(H20) at all temperatures (remember the p s are molar, not mass, densities). For methane pliq(CD4) < pLiq(CH4) only at high temperature. At lower temperatures Pliq(CH4) < pliq(CD4). The critical density of H20 is greater than D20, but for methane pc(CH4) < pc(CD4). Isotope effects are large in the hydrogen and helium systems and pLIQ/ < pLiQ and P > P across the liquid range. Pc < Pc and pc < pc for both pairs. Vapor pressure and molar volume IE s are discussed in the context of the statistical theory of isotope effects in condensed phases in Chapters 5 and 12, respectively. The CS treatment in this chapter offers an alternative description.

The density difference between H2O and D2O can be used for the determination of the deuterium content of heavy water (Schatenstein 1960). It is interesting to note that the 10% difference in density is within 0.5% entirely due to the molecular weight difference. The molar volume of D2O is larger only by 0.34% and that of H2 0 is smaller by 0.15% than the molar volume of H2 0. The isotope effect on the dielectric constant and dipole moment is very small, which plays an important role in the interpretation of solvent isotope effects in aqueous systems (Van Hook 1975). 

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