Energy of Light and Chemical Energy. 22'> 



equilibrium, new heat of reaction, fyc, but the connexion between 

 the logarithm of the constant of equilibrium, the heat of reaction, 

 absolute temperature, will always, nevertheless, be governed by 

 the same law. Since different intensities and different wave- 

 lengths differently affect the values of the chemical and 

 light-kinetic potentials, &c, they will evidently also differently 

 change the values of the different parts of the equation (II). 



Thus, having a reversible system n 1 a 1 + n 2 <T 2 = ^;]0"3, and 



an equation niOV + A/) "^^(/V + ^O = "sf/V + ^O bi light 

 instead of tij^ -\-n 2 u 2 = ft 3 At 3 in the dark, it will depend upon 

 the values of the individual potentials of all components 

 in which direction the equilibrium will shift. The same will 

 be the case when the system is brought from light of one 

 intensity or composition into light of another intensity or 

 composition, the point of equilibrium being for given 

 conditions always a fixed one. 



A short notice in a letter from Professor van't Hoflf leads 

 me to think that a general u principle of movable equilibrium " 

 can be established for light, as it was set up by vant Ho f for 

 heat. I am not sure that this was what van't Hoff meant. 

 In the system C0 + C1 2 = C0C1 2 , H 2 + C1 2 = 2HC1, it is the 

 Cl 2 which absorbs light most. Having a system CO, Cl 2 , 

 COCl 2 or H 2 , Cl 2 , HC1 in the dark, they do not act one upon 

 another, but on exposure to light COCl 2 or HC1 is formed, 

 i. <?., the system is shifted from the left to the right. Again, 

 in the system AgCl (in light) = Ag + Cl 2 (in light), it is the 

 AgCl which absorbs light most, and the light has the effect 

 of forming Ag and Cl 2 from AgCl, and not the opposite. 

 Since all substances absorb light, this lerds to the conclusion 

 that " each kind of equilibrium between two states of matter 

 (system) becomes at a constant volume on exposure to light 

 shifted in the direction which is accompanied by the greater 

 absorption of light/ 3 Van't HofPs principle for heat, para- 

 phrased, is : " Each kind of equilibrium between two different 

 states of matter ( system) becomes at a constant volume on 

 exposure to a higher temperature (heat) shifted in the 

 direction which is accompanied by the absorption of heat." 



From the above principle, further conclusions can be drawn 

 about the influence which the intensity of light and its composi- 

 tion must have upon the point of equilibrium. The greater the 

 intensity of light, the greater the influence of a given wave- 

 length upon the constituents of the system, the greater is the 

 maximum kinetic energy stored in the atoms and molecules. 

 and it is natural to expect that the substance which absorbs 

 light most has also a greater increase in the values of th,» 





