Introduction - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 4

1.4 CHEMICAL THERMODYNAMICS AND KINETICS
IN ENVIRONMENTAL ENGINEERING
The environment may be conceptualized as consisting of various compartments.
Table 1.1 summarizes the total mass and surface areas of various compartments in
the natural environment. The transport of materials between the compartments on
a global scale depends only on forces of global nature. However, on a local scale
the partitioning and transport depend on the composition, pressure, temperature, and
other variables in each compartment.
There are four distinct environmental compartments: hydrosphere, atmosphere,
lithosphere, and biosphere (Figure 1.2). These may be in continuous contact with a
sharp boundary between them (air-water) or may be discontinuous (e.g., soil-water).
In some cases, one phase will be dispersed in another (e.g., air bubbles in water,
fog droplets in air, aerosols and dust particles in air, colloids suspended in water,
oil droplets in water, and soap bubbles in water). Some compartments may have
the same chemical composition throughout, but differ significantly in their spatial
characteristics (e.g., the lower troposphere versus the upper stratosphere, a stratified
deep water body, or a highly stratified atmosphere). The biosphere, which includes
all plant and animal species, is in contact with the three other compartments in the
overall scheme. Reactions and transformations occur in each phase, and the rate of
exchange of mass and energy between the compartments is a function of the extent
to which the respective compartments are in nonequilibrium.

1.4.1 A PPLICATIONS OF T HERMODYNAMICS AND K INETICS

1.4.1.1 Equilibrium Partitioning

Chemical thermodynamics is central to the application of the equilibrium-partitioning
concept to estimate pollutant levels in environmental compartments. It assumes that
the environmental compartments are in a state where they have reached constant

TABLE 1.1
Composition of Natural Environment

Compartment Value
Air (atmosphere) (mass) 5.1 × 10 18 kg
Water (hydrosphere) (mass) 1.7 × 10 21 kg
Land (lithosphere) (mass) 1.8 × 10 21 kg
Land (area) 1.5 × 10 14 m 2
Water (area) 3.6 × 10 14 m 2
Source: Weast, R.C. and Astle, M.J. (Eds). 1981. CRC
Handbook of Chemistry and Physics , 62nd ed.
Boca Raton, FL: CRC Press, Inc.; Stumm, W.
and Morgan, J.J. 1981. Aquatic Chemistry , 2nd
ed. NewYork, NY: John Wiley & Sons, Inc.