[Ostwald on catalysis]

Zeitschrift für physikalische Chemie
volume 15, pages 705-706 (1894)

[Reader's Note: Ostwald chose to state his theory of catalysis in the course of an abstract which he prepared for an article by F. Stohmann on the heats of combustion of foodstuffs. He disagreed with Stohmann's definition of catalysis and so devoted most of the abstract to a discussion of his own ideas.]

After a historical introduction the author brings together the essential values for the heat of combustion of the most important ingredients of nutrients as determined by him and his students. Some general considerations of this are discussed in which the author points out in a praiseworthy manner the great significance of catalytic phenomena for physiology. After a summary of the views of different investigators on this problem, he formulates his own, in which he defines catalysis in the following way:

"Catalysis is a condition of movement of the atoms in a molecule of a labile body which follows the entrance of the energy emitted from one body into another and leads to the formation of more stable bodies with loss of energy."

The abstractor has several objections to make to this definition. First, the assumption of a "condition of movement of the atoms in a molecule " is hypothetical and therefore not suitable for purposes of definition. Also, that is plainly not a loss of energy. What is more, in describing characteristic conditions of catalysis, a loss of free energy can follow under conditions even of absolute energy uptake.

If the abstractor were to formulate for himself the problem of characterizing the phenomenon of catalysis in a general way, he would consider the following expression as probably most suitable: Catalysis is the acceleration of a chemical reaction, which proceeds slowly, by the presence of a foreign substance. It would then be necessary to give the following explanations.

There are numerous substances or combinations of substances which in themselves are not stable but undergo slow change and only seem stable to us because their changes occur so slowly that during the usual short period of observation they do not strike us. Such substances or systems often attain an increased reaction rate if certain foreign substances, that is, substances which are not in themselves necessary for the reaction, are added. This acceleration occurs without alteration of the general energy relations, since after the end of the reaction the foreign body can again be separated from the field of the reaction, so that the energy used up by the addition can once more be obtained by the separation, or the reverse. However, these processes, like all natural ones, must always occur in such a direction that the free energy of the entire system is decreased.

It is therefore misleading to consider catalytic action as a force which produces something which would not occur without the substance which acts catalytically; still less can it be assumed that the latter performs work. It will perhaps contribute to an understanding of the problem if I especially mention that time is not involved in the idea of chemical energy; thus if the chemical energy relations are such that a definite process must occur, then it is only the initial and final states, as well as the whole series of intermediate given states which must be passed through, which must occur, but in no way is the time during which the reaction takes place of concern. Time is here dependent on conditions which lie outside the two chief laws of energetics. The only form of energy which contains time in its definition is kinetic energy, which is proportional to the mass and the square of the velocity. All cases in which such energies take a fixed part are therefore completely determined in time if the conditions are given; but all cases in which the vibrational energy does not play this role are independent of time, that is, they can occur without violating the laws of energy in any given time. Catalytic processes are empirically found to be of the type in which this last property is observed; the existence of catalytic processes is to me therefore a positive proof that chemical processes cannot have a kinetic nature.

W. O.