A system of physical chemistry - Index of

A SYSTEM OF PHYSICAL CHEMISTRY

**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'a

'^ 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

A.

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—

-livjkr.

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

and

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.