CHEMICAL See also:

• ACTION

For example, the question whether a See also:

• SALT (a common Teutonic word, cf. Dutch zout, Ger. Salz, Scand. salt; cognate with Gr. &Xs, Lat. sal)
• SALT, SIR TITUS, BART

On the other hand, especially powerful See also:

• AFFINITIES

T2A'1+A'2+ ... ; this is a See also:

• SPECIAL

. represent the spatial concentrations, i.e. the number of See also:

• GRAM

The conception that the equilibrium is not to be attributed to See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

. .; this states the fundamental law of chemical See also:

• KINETICS (from Gr. taveiv, to move)

. . , and the reaction-velocity corresponding to it is therefore v=kCi1C'z ..., and similarly the opposed reaction-velocity is 1 2 the resultant reaction-velocity, being the difference of these two partial velocities, is therefore V=v-v'=kC1'CE ... -k'Cln"C2"'2... This is the most general expression of the law of chemical mass-action, for the case of homogeneous systems. Equating V to zero, we obtain the equation for the equilibrium state, viz. =k/k'=K; K is called the " equilibrium-constant." Law of chemical statics. Law of chemical kinetics. These formulae hold for gases and for dilute solutions, but assume the system to be homogeneous, i.e. to be either a homo-Limlta- geneous gas-mixture or a homogeneous dilute solution. Lions and The case in which other states of matter See also:

• SHARE (O. Eng. scearu, chiefly in compounds, e.g. land-scearu, a share of land, from sceran to cut; cf. " shear" )

Guldberg and Waage expressed this in the form " the active mass of a solid substance is constant." The same is true of liquids when these participate in the pure state in the equilibrium, and possess therefore a definite vapour-pressure or solubility. When, finally, we are not dealing with a dilute solution but with any kind of mixture whatever, it is simplest to apply the law of mass-action to the gaseous mixture in equilibrium with this. The composition of the liquid mixture is then determinable when the vapour-pressures of the separate components are known. This, however, is not often the case; but in principle this consideration is important, since it involves the possibility of extending the law of chemical mass-action from ideal gas-mixtures and dilute solutions, for which it primarily holds, to any other system whatever. The more See also:

• RECENT

Essentially, Berthollet's See also:

• IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

See also:

• WILLARD, FRANCES ELIZABETH (1839–1898)

We will now apply these conclusions to the theory of the ignition of an explosive gas-mixture, and in particular to the See also:

• COMBUSTION (from the Lat. comburere, to burn up)

See also:

• ACETYLENE

First we have the condition of slow combustion; the heat is conveyed by conduction to the29 adjacent layers, and there follows a velocity of propagation of a few metres per second. But since the combustion is accompanied by a high increase of pressure, the adjacent, still unburnt layers are simultaneously compressed, whereby the reaction-velocity increases, and the ignition proceeds faster. This involves still greater compression of the next layers, and so if the mixture be capable of sufficiently rapid combustion, the velocity of propagation of the ignition must continually increase. As soon as the compression in the still unburnt layers becomes so great that spontaneous ignition results, the now much more pronounced compression-waves excited with simultaneous combustion must be propagated with very great velocity, i.e. we have spontaneous development of an " explosion-wave.” M.P.E. See also:

• BERTHELOT, MARCELLIN PIERRE EUGENE (1827–1907)

Dixon. Hydrogen and oxygen, H2+O . 28to 2821 Hydrogen and nitrous See also:

• OXIDE

As is well known, this phenomenon is specially striking in the case of hydrogen, which may therefore be taken as a typical example. The law of mass-action affirms the action of a substance to be the greater the higher its concentration, or, for a gas, the higher its partial-pressure. Now experience teaches that those metals which liberate hydrogen from acids are able to See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

If this be coupled with the law that the solubility of solid substances, as with vapour-pressures, is independent of the presence of other electrolytes, it is sufficient to know the solubilities of the electrolytes in question, in order to be able to determine which substances must participate in the equilibrium in the solid state, i.e. we arrive at the theory of the formation and solution of precipitates. As an See also:

• ILLUSTRATION

See also:

• ARRHENIUS, SVANTE AUGUST (1859– )

Now the degree of electrolytic dissociation changes with concentration in a See also:

• REGULAR

See also:

• CATALYSIS (from the Gr. Kara, down, and Meta, to loosen)

A catalyte must therefore always accelerate the reverse-reaction. If the velocity of formation of a body be increased by addition of some substance then its velocity of decomposition must likewise increase. We have an example of this in the well-known fact that the formation, and no less the saponification, of See also:

• ESTERS

The action of a colloidal-platinum solution on the decomposition of hydrogen peroxide is still sensible even at a dilution of 1/70,000,000 grm.-mol. per litre; indeed the activity of this colloidal-platinum solution calls to mind in many ways that of organic ferments, hence Bredig has called it an " inorganic ferment." This See also:

• ANALOGY (Gr. avaXo-yLa, proportion)

Since we are not in a position to measure directly the intensity of chemical forces, the idea suggests itself to determine the strength of chemical affinity from the amount of the work which the corresponding reaction is able to do. To a certain extent the evolution of heat accompanying the reaction is a measure of this work, and attempts have been made to measure chemical affinities thermo-chemically, though it may be easily shown that this definition was not well chosen. For when, as is clearly most convenient, affinity is so defined that it determines under all circumstances the direction of chemical change, the above definition fails in so far as chemical processes often take place with absorption of heat, that is, contrary to affinities so defined. But even in those cases in which the course of the reaction at first proceeds in the sense of the evolution of heat, it is often observed that the reaction advances not to completion but to a certain equilibrium, or, in other words, stops before the evolution of heat is complete. A definition free from this objection is supplied by the second law of thermodynamics, in accordance with which all processes must take place in so far as they are able to do external work. When therefore we identify chemical affinity with the maximum work which can be gained from the process in question, we reach such a definition that the direction of the process is under all conditions determined by the affinity. Further, this definition has proved serviceable in so far as the maximum work in many cases may be experimentally measured, and moreover it stands in a simple relation to the equilibrium constant K. Thermo-See also:

• DYNAMICS
• DYNAMICS (from Gr. bbvayts, strength)

Hence it seems possible to calculate equilibria for low temperatures from heats of reaction, by the aid of the two equations A=Q, A=RT log K; and since the change of A with temperature, as required by the principles of thermodynamics, follows from the specific heats of the reacting substances, it seems further possible to calculate chemical equilibria from heats of reaction and specific heats. The circumstance that chemical affinity and heat-evolution co nearly coincide at low temperatures may be derived from the See also:

• HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

We hence arrive at the result that an equation of the form reaction-velocity =chemical force/chemical resistance must also hold for chemical change; here we have an analogy with See also:

• OHM, GEORG SIMON (1787-1854)

At higher temperatures the reaction always proceeds, at least in homogeneous systems, to a certain equilibrium, and as the chemical resistance now has finite values this equilibrium will always finally be reached after a longer or shorter time. Finally, at very high temperatures the chemical resistance is in every case very small, and the equilibrium is almost instantaneously reached; at the same time, the affinity of the reaction, as in the case of the mutual affinity between oxygen and hydrogen, may very strongly diminish, and we have then chemical indifference again, not because, as at low temperatures, the denominator of the previous expression becomes very great, but because the numerator now assumes vanishingly small values. (W.