Page:Text-book of Electrochemistry.djvu/100

 molecule of ammonium chloride so formed work will be done which amounts to pv = BT = I'QOTcal.

Now allow the ammonium chloride to pass isotheimally from concentration Cq to concentration C^ and the work done wiU be —

The ammonium chloride is then forced at this pressiure into the second vessel, where it decomposes into cunmonia and hydrochloric acid at pressures C4 and Ci respectively, and no work has to be done to accomplish this (exactly as in the case of the evaporation of water where no work is done, but there is a loss of heat). The new quantities of ammonia and hydrochloric acid at the pressures C4 and Cs are now removed, each through a semi-permeable waU.

The work done for the gram-molecule of cunmonium chloride is ^i? = BT, and that done by the gram-molecule of each of the gases, ammonia and hydrochloric acid, iapv ss BT. Finally, if the gram-molecule of ammonia and that of hydro- chloric acid are allowed to expand isothermally &om pressure C4 to Ci or from C5 to C2 in the different cases, the original condition is established. During this last process the work done will be —

Ai = BTln ^ and ^2 = BTln %

During the cycle certain amounts of work are done on the system, and equal quantities are regained at other points in the process, but there still remain -A, A\, A%, Since the cycle was carried out at constant temperature and completely reversibly the sum of these three quantities must be zero. We therefore obtain the equation —

- Jl + ^1 + ^2 = = -iZrAn g - In g* - In ^\ or— C'l X ^2 = AjCs and C4 x C's = kC^

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