Geology Reference
In-Depth Information
1.0
E
H
, V
Fe
3+
0.8
0.6
0.4
Fe
2
O
3
0.2
Fe
2+
0.0
-0.2
-0.4
Fe
3
O
4
-0.6
Fe
-0.8
-1.0
0
1
2
3
4
5
6
7
8
9
10
11 12 13
14
pH
Fig.9.4PourbaixDiagramforironoxidesinaqueoussolution.RedrawnfromHayes(2003)
natural scientist to a wider audience in the assessment of mineral resources is by
using exergy instead. Like the others, it is derived from the Second Law.
Yet whilst entropy and Gibbs free energy may describe energy changes between
two opposing systems, exergy does so when one is fixed and defined. Such fixed
and defined system is subsequently referred to as a reference environment (R.E) or
surrounding environment and the potential for change of a thermodynamic system
with respect to this R.E. is named exergy.
9.5.1 General definition
Technically, exergy (denoted by B) is defined as the maximum amount of work that
may theoretically be performed by bringing a system into equilibrium with its sur-
rounding environment by a sequence of reversible processes. Exergy analysis helps
to pinpoint the irreversibilities throughout systems, thereby becoming a powerful
tool for improving their e
ciency. This leads to resource savings and fewer emis-
sions and wastes entering the surrounding environment. Furthermore it can also be
applied to the assessment of natural resources as is done in this topic.
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