Dairy Chemistry And Biochemistry

296 DAIRY CHEMISTRY AND BIOCHEMISTRY

Table 7.2 Physical constants of water and ice (from Fennema, 1985)

Molecular weight

Phase transition properties

Melting point at 101.3 kPa (1 atm)

Boiling point at 101.3 kPa (1 atm)

Critical temperature

Critical pressure

Triple point

Heat of fusion at 0°C

Heat of vaporization at 100°C

Heat of sublimation at 0°C

18.01 534

0.ooo"c

100.00"C

374.15"C

22.14 MPa (218.6 atm)

0.0099'C and 610.4 kPa (4.579 mmHg)

6.012kJ (1.436kcal)mol-'

40.63 kJ (9.705 kcal) mol-

50.91 kJ (12.16kcal) mol-'

Other properties at 20°C 0°C 0°C (ice) - 20°C (ice)

Density (kg I-') 0.9998203

Surface tension against 72.75 x

Vapor pressure (Pa) 2.337 x lo3
Specific heat (J kg-' K-I) 4.1819
Thermal conductivity 5.983 x 10'

Thermal diffusivity (m2 s-I)
Dielectric constant,

Viscosity (Pa s) 1.002 x 10-3

air (N m-I)

(J m-'s-' K-' 1

1.4 x

static" 80.36

at 3 x lo9 Hz 76.7

(25'C)

0.999841

1.787 x

75.6 x 10-3

6.104 x 10'

4.2177

5.644 x 10'

1.3 10-5

80.00

80.5

(1 .5"C)

0.9168

6.104 x 10'

2.1009

22.40 x lo2

• 1.1 x 10-4
  91b
  
  
  • (- 12°C)
  
  
  
  

0.9193

1.034 x 10'

1.9544

24.33 x 10'

• 1.1 x 10-4
  98b
  3.2


• 
  

"Limiting value at low frequencies.
bParallel to c-axis of ice; values about 15% larger if perpendicular to c-axis.

Table 7.3 Properties of water and other compounds (from Roos, 1997)

Hydrofluoric Hydrogen
A m m o n i a acid sulphide Methane Water
Property (NH,) (HF) W2.T (CHJ (HZO)

Molecular weight 17.03 20.02 34.08 16.04 18.015
Melting point ('C) - 77.7 -83.1 - 85.5 - 182.6 0.00
Boiling point ("C) - 33.35 19.54 - 60.7 -161.4 100.00
Critical T ("C) 132.5 188.0 100.4 -82.1 374.15
Critical P (bar) 114.0 64.8 90.1 46.4 221.5

molecules which, due to the above-mentioned differences in electronegativ-
ity, have some of the characteristics of bare protons. Thus, each water
molecule can form four hydrogen bonds arranged in a tetrahedral fashion
around the oxygen (Figure 7.ld). The structure of water has been described
as a continuous three-dimensional network of hydrogen-bonded molecules,
with a local preference for tetrahedral geometry but with a large number of
strained or broken hydrogen bonds. This tetrahedral geometry is usually