The shear fluidity PHI(S) = 1/eta(S), of liquid water at fixed molal volume [(i) V(4-degrees-C, 1 atm) = 18.02 and (j) V = 17.76 cm3/mol] was treated by the generalized equilibrium B = U. B refers to bonded and U to "unbonded". [U] + [B] = constant, [U] = c-PHI(S), and c is a proportionality constant. In K plots were found to be precisely linear in T-1 (0-200-degrees-C), e.g., ln K'= ln [PHI(S)/(6.148 - PHI(S))] = ln [(1 - x(B)')/x(B)'] = -2446.92 T-1 + 6.68448. (6.148 is the high-temperature PHI(S) limit.) The enthalpy almost-equal-to energy and entropy changes for the B = U process are thus 4.86 kcal/mol and 13(.3) eu, i.e., twice those per hydrogen bond from Raman measurements; 2.5 kcal/mol O-D...O from 20 to 400-degrees-C1 and 6.2 cal/(deg mol) O-H...O.2. All hydrogen bonds restraining a water molecule eventually break and re-form as it tumbles during shear. Two hydrogen bonds break, stoichiometrically, per H2O molecule in the complete dissolution of the tetrahedral network. The shear viscosity process thus appears to involve net motion of H2O molecules between different sites. The constant-volume heat capacity, (V)C(V), was determined at V = 18.01578 cm3/mol. Thermodynamic analysis employing the temperature dependence of one-bond x(B) values yielded a high-pressure (almost-equal-to 2 kbar) homogeneous nucleation temperature, T(H), of almost-equal-to 170 +/- 10 K (181 K measured, x(B) = 0.97), where the calculated nonrelaxational contribution to (V)C(V) is maximal. The present treatment of PHI(S) and (V)C(V) (with [U] = c-PHI(S), the energy change of 2.4 kcal/mol O-H...O, the entropy change of almost-equal-to 6.6 cal/(deg mol) O-H...O, the almost-equal-to 170 K T(H) value) and the Raman data are thus all consistent. Also, the volume change for the B = U process is very small, as seen from high-pressure Raman measurements; 9 kbar, room temperature; 23 kbar, 100-260-degrees-C (this work and refs 3 and 4) and to 400-degrees-C1. The temperature dependence of (V)C(V) at three constant molal volumes, 18.01578, 17.9109, and 17.5636 cm3/mol is of the form (V)C(V)T2 = -A + BT - CT2. Energy fluctuations were obtained versus T from (E - EBAR)2 = (V)C(V)k(B)T2 = k(B)(-A + BT - CT2) (N,V,T ensemble), The ratio of the third moment of the energy fluctuation (skewness) to the second moment (width) is M(3)/M(2) = E - EBAR)3/(E - EBAR)2 almost-equal-to Bk(B)/(V)C(V). This ratio rises at temperatures above the maximum in (V)C(V), as hydrogen bond breakage becomes increasingly important. Detailed treatment of the total, relaxational, and nonrelaxational, second, third, and fourth central moments of the canonical energy distribution is included, which indicates that large positive relaxational energy fluctuations refer to hydrogen bond breakage, e.g., wide librational fluctuations yielding high-energy bifurcated structures.
