Inorganic chemistry / by Edward Frankland and Francis R. Japp.

Date:
1884
Catalogue details

Licence: Public Domain Mark

Credit: Inorganic chemistry / by Edward Frankland and Francis R. Japp. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    131/854 (page 103)
    This reaction liberates 12,200 cal., if all the compounds are in solution, and 45,600 cal. if they are in the solid state- In the same way, one acid expels another from its salts, when it liberates more heat in combining with the same base; at least, this is so in all cases where each of the acids forms only one salt with the base. But all these relations are only then strictly true, when the heat liberated by the acids, bases, and salts is calculated for these bodies in the same physical condition, namely, the solid state. The following example will show how a change of physical condition and the special combiaations formed with the solvent may affect the result. Gaseous hydrochloric acid acts upon dry mercuric cyanide, forming mercuric chloride and hydrocyanic acid— 2HC1 + HgCy2 = 2HCy + HgCl^.. +10,600 cal. But hydrocyanic acid in solution acts upon mercuric chloride in solution, forming mercuric cyanide and hydrochloric acid. This reversal of the reaction is explained by the fact- that two molecules- of hydrocyanic acid in solution liberate in acting upon mercuric oxide 31,000 cal., whilst a solution of hydrochloric acid liberates only 19,000 cal. There are therefore +12,000 cal. liberated in the reaction in the wet way, a result which experiment completely confirms. Theory, therefore, predicts this reversal of the reaction corresponding to the change in the thermal sign. This change is due to the intervention of a new chemical reaction attended by liberation of heat, the combination of gaseous hydrochloric acid with water, by which the hydrochloric acid has yielded up a portion of its energy. The same principle of maximum work enables us to produce a number of compounds which could not be obtained directly, because their formation is attended with a,bsorption, and their decomposition with liberation of heat. This end is attained by the device of a double decomposition bringing about the simul- taneous formation of some other compound, the production of which is attended with a liberation of heat greater than the absorption Hydrochloric acid. Mercuric cyanide. Hydrocyanic acid. Mercuric chloride.