A system of physical chemistry - Index of


A system of physical chemistry - Index of


system which is accompanied by a small change in the entropy of the

matter and in the entropy of the radiation, finally obtaining as a

criterion of the above equilibrium state, the relation—


'^ A

where a stands for a complex expression, involving the temperature T

of the gas (which is independent of the temperature T^ of the radiation),

€ is the quantity of energy absorbed per molecule of substance mi, the

energy being in the form of monochromatic radiation vo, the density of

the radiation being p, and N the number of molecules in i gram-


molecule. Since T5 and p are independent of the gas temperature T,

the magnitudes -— and « must also be independent of T. Since these


quantities are also independent of T^, we arrive at the same relation

between p and Tj as is expressed in Wien's radiation formula." Since

Wien's formula only holds for the short wave region, Einstein's relation

in the first instance is likewise restricted to this region. "If we write

Wien's radiation formula after introducing the Planck constants h and

k, we obtain—


and on comparing this with the previous equation, we see that—


A'a Stt/^i'o^

A r*

The most important consequence of the above is that e = ^v,,,

which shows that one gas molecule which decomposes under radiation

of frequency vq absorbs in its decomposition just /lu^ of energy, i.e. 1

quantum, as a mean value.

Bodenstein {/oc. cit.) has collected the results of a number of in-

vestigations carried out by various authors, with the object of showing

how far the law of the photochemical equivalent is borne out by experiment.

That it is so at least is approximately shown by the following

table :—

Reaction Studied.

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