380 



EEPOET 1886. 



(54) In chemical reactions among electrolytes those bodies are in general 



formed in greatest quantity, the formation of which is accompanied by 

 the greatest heat-production. 



This is the ' principle of maximum work,' modified. It is valid in general, 

 not always. 



[Neglecting now the above process 4, the author points out that process 2 has 

 two parts, one concerned with the acid only, the other with the base only. Call 

 these 2a and 2b. Processes 1 and 3 he considers all along as giving a constant 

 thermal eflect ; and so he splits up the total heat-productiou H, by all the processes, 

 thus — 



H-^S = (Aj + A3) + A,a + Ajj, 



and states — ] 



(55) The heat produced by the neutralisation of an acid A by a base B (less 



heat of possible solidification) is equal to a constant, plus a term de- 

 pending on the nature of the acid only, plus another depending only on 

 the nature of the base. 



This has beeu verified by the experiments of M. Thomsen. A table of the heats 

 of formation of some salts from the results of Berthelot and Thomsen are given. 

 It is on such numbers as these that the rule of Thomsen is founded. 



Seats of formation of some salts in dilute solutions. 



§ 21. Heat of activity. 



This is the name given to the heat used in transforming a body from inactive 

 •to active state. 



Now if an acid unites with a base, one can regard the process as the displace- 

 ment of a feeble acid (water) from its salt (basic hj^drate) by a stronger acid. 

 Then, if every substance concerned were perfectly active, the heat of neutralisa- 

 tion of water ought to be the same as that of the strong acid, according to the 

 hypothesis at the beginning of last section, and so no heat-production should result 

 from the interchange. But if the water, as fast as formed, passes into an inactive 

 state, its heat of activity will be set free. In fact, it is necessary to suppose that 

 water immediately after its formation is perfectly active, for it is formed by the 

 collision of two ions H and OH, endowed with movement. But this activity is in- 

 stantly lost, and almost inactive ordinary water results. Thus we have shown that — 



(66) The heat of neutralisation, set free by the transformation of a perfectly 

 active base, and perfectly active acid, into water and simple salt, is only 

 the heat of activity of the water. 



One might call this the thermoneutrality of perfectly active electrolytes. It is 

 intimately connected with the Williamson and Clausius hypothesis. For as it is 

 reckoned, by this hypothesis, a fair chance whether an ion encounters a similar 

 or a dissimilar one, no work can be done by mere interchanges of ions. 



Inactivity of salts is founded on complexity, and to maks them more active 

 one must split up molecular complexes. Inactivity of hydrates is caused by more 

 or less disaggregating the molecule into its ions. Either process consumes energy. 

 Elevation of temperature partly effects the process and does the necessary work 

 in liquids, though not in solids, for solids have no appreciable activity even when 

 'warm. So it is natural to expect that the specific heat of a substance in the liquid 

 £tate should be decidedly greater than in the solid state, at least for electrolytes. 



