Sign of the Chemical Potential

At first, this seems surprising because we know that the chemical potential of an element at standard cmiditions is zero, i.e., = 0. This is of course also valid for 

When H2 and H are present at standard conditions and equilibrium has been established, the chemical potential of the electrons, fp e ), is supposed to be zero. (The electron potential yu(e ), abbreviated will be discussed in more detail in Chap. 22.) Because y (H2 g) disappears by definition, it follows necessarily that in a state of equilibrium, y (H+ w) has to be zero as well. 

If we use values of chemical potentials in the following, they are valid for room conditions and for dissolved substances of concentrations of 1 kmol m (= 1 mol L ) where water is the usual solvent. Elements in their usual, stable state receive, as agreed, the value /i = 0 (see also Table 4.3 at the end of this chapter or Sect. A.2.1 in the Appendix). This is for example valid for molecular hydrogen (H2 g) = 0, while atomic hydrogen has a rather high positive potential y (H g) = +203kG. This means that its tendency to transform into H2 is very strong. 

A look at Table 4.3 and Sect. A.2.1 in the Appendix shows something remarkable. Most of the potential values are negative. A substance with negative chemical potential can be produced spontaneously from the elements because it has a weaker tendency to transform than the elements it is produced from. However, this also means that most substances do not tend to decompose into their elements but, in 

Experiment 4.4 Decomposition of SuNn. A small amount of tetrasulfur tetranitride explodes (like a cap for use in toy guns) when hit lightly with a hammer. 

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