The energy hump in chemistry. II

Abstract 1. 1. There are two energy humps for hydrogen. The one in the reaction from hydrogen to hydrogen gas varies with the nature of the cathode metal and is measured in each case by the over-voltage. The one from molecular hydrogen to hydrogen ion depends on the reducing power of molecular hydrogen. It apparently varies from about 1.1 volts in neutral solutions to about 1.2 volts in alkaline solution and to about 1.4 volts in acid solution. Platinized platinum removes both humps and consequently makes the hydrogen electrode a reversible one instead of being in the class with the chlorate-chloride electrode. The reason for the reaction between molecular hydrogen and silver oxide is not yet clear. 2. 2. Since raising the temperature and increasing the concentration lower the energy hump, it is not surprising that Ipatiew was able to reduce copper and nickel salts with hydrogen at or above certain temperatures and certain pressures. It is probably not true, as Ipatiew assumed, that there is a critical temperature below which hydrogen will not reduce copper sulphate. 3. 3. Foerster's method of determining apparent reduction potentials gives the true values but does not show the activating effect of the metals. Conant's method gives the apparent reduction potentials in presence of metals; but does not give the true values except when there is no activation by the metal. It is wiser to try both methods in any doubtful case. 4. 4. From existing data the energy hump for oxygen is probably about 0.3 volt in acid solution and about 0.36 volt in alkaline solution. 5. 5. We have shown that a concept similar to the one employed by Arrhenius to account for the temperature coefficients of reaction velocities can also be applied to all cases of contact catalysis at constant temperature. The important thing, however, is that we have shown that all cases of contact catalysis may be considered from a single view-point. Contact catalysis, solvent catalysis, hydrogen-ion catalysis, water-vapor catalysis, and the catalytic decomposition of manganese dioxide have hitherto been treated as five distinct cases. Whether hydrogen-ion catalysis is ever a solvent catalysis is debatable; but it is a point of view which should be stimulating. 6. 6. A catalytic agent may act like a siphon and not like a lubricant as postulated by Wilhelm Ostwald. If a catalyst acts like a siphon, it can and often does initiate a reaction. It will change the apparent reduction potential. 7. 7. Potassium chlorate and potassium perchlorate are theoretically stable at room temperature. Molecular hydrogen will never reduce sodium sulphate or a solution of sodium sulphate at room temperature in the absence of a catalyzer. 8. 8. Since an electromotive force is an equilibrium phenomenon, it is independent of any change of molecular distribution which does not change the chemical potential. Addition of a catalytic agent may increase the rate at which the electromotive force develops; but it cannot change the absolute value. 9. 9. The apparent chemical potential is measured by means of reaction velocities and consequently can theoretically have any value between that in the presence of no catalyst and the true chemical potential as given by the free energy. 10. 10. The physical-chemical fairyland, in which all reactions permitted by free-energy relations will always take place at least in fancy, owes its existence to a false assumption as to catalytic agents and to unlimited extrapolation of two approximation equations-the van't Hoff rule for temperature coefficients of reaction velocities and the Maxwell-Boltzmann distribution. This is not science. 11. 11. Reactions may be divided broadly into three groups with no sharp dividing lines between the groups. (I) Many or all of the reactant molecules are in an activated state, in which case the reaction velocity is very great Many of these are ion reactions. (z) Relatively few of the reactant molecules are in an activated state, in which case the reaction velocity is very small. These are the fashionable reactions to study at present. (3) None of the reactant molecules are in an activated state, in which case the reaction velocity under ordinary conditions is zero. These are the reactions which will be studied intensively in the next decade.