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.

    115/854 (page 87)
    Extent and intensity of affinity are quite independent of each other Thus copper and mercury in the compounds CuO and HgU have the same extent of affinity for oxygen; but since mercuric oxide breaks up at a relatively low temperature into its constituents, whereas cupric oxide does not undergo decomposition until a tem- perature above 1000° has been reached, and then yields up only a portion of its oxygen, the intensity of affinity for oxygen is mu3h greater in the case of copper. Again, the extent of affinity of carbon towards hydrogen is four times as great as that of chlorine. This may be seen in methylic hydride (CH^) and hydrochloric acid (HCl). But whereas carbon and hydrogen cannot be made to combine directly at all, chlorine and hydrogen unite with evolution of great heat. Here the element of greatest extent of affinity has least intensity of affinity. One atom of phosphorus can unite with three atoms of chlorine, giving off much heat, and forming a compound which may be distilled without decomposition; one atom of silver can unite with only one atom of chlorine, and the resulting compound is decomposed by the action of daylight. Here extent and intensity of affinity go together.* Modes of Chemical Action.—Matter undergoes chemical change in five different ways, viz.:—• 1st. By the direct combination of elements or compounds witli each other. 2nd. By the displacement of one element or group of elements in a body by another element or group of elements. 3rd. By a mutual exchange of elements or groups of elements in two or more bodies. 4th. By the rearrangement of the elements or groups of ele- ments already contained in a body. * The above can be regarded only as an approximately correct statement. In nearly every so-called direct combination of elements there is a preliminary decom- position of elementary molecules :— H2 + CI2 = 2HC1. Here the affinity of. hydrogen for clilorine is the force which strives to bring about the reaction, and in this it is opposed by the two affinities of hydrogen for hydrogen and of chlorine for chlorine, which have to be overcome before the reaction can occur. Thus, the apparently lower affinity of carbon for hydrogen may in reality consist in a higher affinity of carbon for carbon—the affinity of hydrogen for hydrogen remaining, of course, the same in both reactions. For the same reason the heat of combination is a complex quantity, and cannot be regarded as an infallible measure of the intensity of affinity (see Thermo- chemistry).