Indicators, energy balance definition

The purpose of defining standard free energies of formation is to use these individual reference values to determine standard free energies of reaction, AG°, where the subscript r indicates reaction. By definition, AG° is the free energy change attending a balanced chemical reaction that involves substances at their standard states... 

The value of E in relation to like the value of gj, indicates the evaporative nature of the surface so E < E q or E/Ee, < 1 reflects surface dryness or stomatal closure as well as the balance of energy exchange between the atmosphere and the underlying surface. By definition, E > Ef, can be caused only by advection. As implied above with respect to the partitioning of temperature, this may also result from the entrainment of dry air from above the convective boundary layer that develops daily over the earth surface. To further illustrate the relation between E and Ef, in terms of surface characteristics, it is helpful to write the Penman-Monteith equation (Monteith and Unsworth, 1990),... 

A final set of definitions leads to the classification of the types of systems. One can distinguish three types. The first is the open system. In such a system mass and energy flux may occur across the boundaries, as indicated by the open sample crucible in Fig. 2.1. The experimental set up of thermogravimetry is a typical example of an open system. The open sample crucible in Fig. 2.1 is placed on a temperature controlled balance. The sample to be analyzed, contained in the crucible, is the system. Across its boundaries flows heat from the furnace, and mass can be lost by evaporation or gained by interaction with the atmosphere. All changes in mass are recorded by the balance. 

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