Joseph William Mellor.

A comprehensive treatise on inorganic and theoretical chemistry (Volume 1) online

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W. Clayton, Trans. Faraday Soc., 11. 164, 1916 ; H. T. Calvert, Ann. Physik, (4), 1. 483, 1900 ;
P. Drude, &., (4), 1. 483, 1900 ; Zeit. phys. Chew., 23. 207, 1897 ; J. Dewar and J. A. Fleming,
Proc. Roy. Soc., 62. 250, 1897.

7 H. C. Jones and C. G. Carroll, Amer. Chem. Journ., 28. 284, 1902 ; H. C. Jones and
G. Murray, ib., 30. 205, 1903 ; H. C. Jones, J. Barnes, and E. P. Hyde, ib., 27. 22, 1902 ; S. Tanatar,
Zeit. anorg. Chem., 28. 255, 1901 ; G. Bredig and H. T. Calvert, Zeit. Elektrochem., 7. 622, 1901 ;
Zeit. phys. Chem., 38. 513, 1901 ; G. Carrara and A. Bringhenti, Gazz. C/iim. Ital, 33. 362, 1903 ;
M. Hanriot, Compt. Rend., 100. 172, 1885 ; M. Berthelot, ib., 95. 8, 1882 ; E. Schone, Liebig'*
Ann., 197. 137, 1897 ; S. Tanatar, Ber., 36. 199, 1903.

8 R, Bottger, Journ. prakt. Chem., (1), 80. 58, 1859; J. W. Briihl, Ber., 28. 2855, 1895;
K. Osikoff and S. Popoff, Journ. Russian Phys. Chem. Soc., 35. 637, 1903.

9 S. Tanatar, Journ. Russian Phys. Chem. Soc., 376. 40, 1908.

10 L. Crismer, Butt. Soc. Chim., (3), 6. 24, 1893.

11 T. H. Walton and H. A. Lewis, Journ Amer. Chem. Soc., 38. 633, 1956, 1916.

10, Quantitative Application of the Law of Mass Action

Chemical phenomena must be treated as if they were problems in mechanics.
L. MEYER (1868).

I. Kant * has said that in every department of physical science there is only so
much science as there is mathematics ; and as our knowledge of natural phenomena
grows more clear and precise, so does it become more and more possible to employ
mathematical methods. Owing to the absence of all mathematical treatment in
chemical phenomena in his time, I. Kant denied to chemistry the name of science.

The most simple type of chemical reaction is one in which individual molecules
are involved in the change ; more complex reactions are concerned with the mutual
action of two or more molecules. For example, in the decomposition of nickel
carbonyl, Ni(CO) 4 ->Ni+4CO, the individual molecules of nickel carbonyl are
independently concerned in the change this type of reaction is called a unimolecular
reaction; with a reaction of the type, H 2 0+COC1 2 ->2HC1 - |-C() 2 , the mutual
action of two molecules is necessary for the reaction, and this is accordingly called
a bimolecular reaction ; and in the formation of ozone, 30 2 >20 3 , the mutual action
of three molecules of oxygen is necessary and this is accordingly called a termolecular
reaction. The back reaction, in the preceding bimolecular reaction, is C0 2 +2HC1
->COCl 2 -}-H 2 0, which is a termolecular reaction. The terms uni-, bi-, ter-, and
multi-molecular, or what is equivalent, mono-, di-, tri-, poly-molecular reaction,
were introduced by J. H. van't Hoff 2 to 'indicate the number of molecules con-
cerned in a reaction. Keactions involving more than two molecules are not very
common. This is easily understood if we assume that bimolecular reactions are
caused by the collision of two molecules, termolecular reactions by the simultaneous
collision of three molecules, etc. The probability of a simultaneous collision between
three molecules is very much less than between two molecules, and the greater
the number of molecules taking part in a given transformation, the more likely is
the reaction to proceed by some other path than by the simultaneous collision of
a large number of reacting molecules.

The decomposition of hydrogen peroxide in light. A solution of hydrogen
peroxide decomposes when it is exposed in a quartz vessel to the rays of light
from a mercury lamp. The decomposition ceases when the light is extinguished.
If the amounts of hydrogen peroxide in the solution exposed for various periods of
time be determined, the rate of decomposition can be calculated. It is found that
if a represents the initial concentration of the solution expressed in gram-molecules
per litre, and x the amount decomposed at the time t, the solution will then
contain a x gram-molecules of the compound in question. Let L. Wilhelmy's
hypothesis, op. cit., be now tested. The velocity of the reaction at any time t
must be equal to k(a x). If the symbol dx be employed to denote the amount


of peroxide decomposed in the minute interval of time dt, the velocity of the
reaction, the amount of substance decomposed in unit time, at the moment t, will
be represented by

f =*(-); A;*i-* ... (1)

The passage from the equation on the left to that on the right involves a
very simple mathematical operation. The expression a-^t(a x) measured at
different intervals of time must be a constant, k, if the reaction progresses so that
only one molecule of hydrogen peroxide is concerned in the process H 2 2 ->H 2 0-fO.
Selecting a few measurements by J. H. Mathews and H. A. Curtis (1914), 3 we get

Time (t) . 100 160 220 310 432

HoO, per cent. (x\ . . . 1'58 1'06 0'83 0'63 0'44 0-2(5

k . . , ' . . . 0-0040 0-0041 0-0042 0-0041 ' 0-0042

The values of k are computed by the substitution of a=l'58, and the corresponding
values of x and t in the second of the above equations. The constancy of the
different values of k is quite consistent with the hypothesis. However, suppose
that the decomposition were to be represented by the usual equation, 2H 2 2
->2H 2 0+0 2 , implying that two molecules of hydrogen peroxide mutually react pro-
ducing water and oxygen molecules. Then the velocity of the reaction must be
represented by

With the same data as before, the values of \ are no longer even approximately
constant. Hence, it is inferred that the decomposition of hydrogen peroxide in
light is a unimolecular reaction, H 2 2 >H 2 0-fO, and not really a bimolecular
reaction, 2H 2 2 -2H 2 0+0 2 , even though the last-named equation is conventionally
used to represent the process in order that attention may be focussed on the initial
and end products of the reaction. The unimolecular reaction is slow enough to be
readily measured. The atoms of oxygen from two different molecules of hydrogen
peroxide unite to form molecular oxygen, 0-f-0=0 2 , far too quickly to influence
the measurement of the unimolecular change. This may be illustrated 4 by the
following analogy :

The time occupied in the transmission of a telegraphic message depends both on the
rate of transmission along the conducting wire, and on the rate of progress of the messenger
who delivers the telegram ; but it is obviously this last slower rate that is of really practical
importance in determining the time of transmission.

Hence the following rule : If a chemical reaction takes place in two stages, one of
which is considerably faster than the other, the observed order of the whole reaction will
be determined by the order of slower change.

The decomposition of hydrogen peroxide in contact with platinum. It has
been found by Gr. Bredig and M. von Berneck (1900) 5 that while the catalytic
decomposition of dilute solutions of hydrogen peroxide say below ~th gram-
molecule per litre by colloidal platinum is undoubtedly unimolecular, H 2 2
-H 2 0+0, more concentrated solutions say above the J gram-molecule per litre
decompose bimolecularly, 2H 2 2 ->2H 2 0+0 2 ; and that with intermediate con-
centrations, both types of reaction prevail. For instance, with a concentration
of 0'0034 gram-molecule of hydrogen peroxide per litre, G. Dyer and A. B. Dale
(1913) 6 find the following values of the constant k :

Unimolecular reaction . . 0'014 0-016 0-015 0-013 0-015 0-015

Birnolecular reaction . . 0*0036 0-0047 0-0048 0*0052 0-0073 0-0090

Th constancy of the values of k in the first case is satisfactory, but not in the second


case. Hence it is inferred that the decomposition of hydrogen peroxide by colloidal
platinum is a uni- not a bi-molecular reaction. Again, with a concentration of 0'145
gram-molecules of hydrogen peroxide per litre, the values of the constant k are :

Unimolecular reaction . . 0-0075 0-0068 0-0062 0-0057 0*0051 0-0054
Bimolecular reaction . . 0'0015 0-0015 O'OOIS 0'0015 0'0014 0-0016

Here the fluctuations in the value of the so-called constant show that the decom-
position of the hydrogen peroxide is undoubtedly a bi- and not a uni-molecular
process. The decomposition of hydrogen peroxide by heat similarly follows the
bimolecular law. To summarize, the decomposition of hydrogen peroxide in light,
and when stimulated by colloidal platinum in dilute solutions, is a unimolecular
process ; and when decomposed by heat, or by colloidal platinum in concentrated
solutions, it is a bimolecular process. It has also been found that the velocity of
the photochemical decomposition of hydrogen peroxide is proportional to the
radiant energy absorbed. The energy absorbed during the decomposition of a
gram-molecule of hydrogen peroxide is nearly equal to that given out by the decom-
position of the substance in darkness.

The decomposition of steam by red-hot iron. Let 'the method just developed
be applied to the reaction of steam on red-hot iron previously described ; and
let C 0) C 1} C 2) C$ respectively denote the concentrations of the iron, steam, hydrogen,
and iron oxide at any time t.

3Fe+4H 2 O =4H 2 +Fe 3 O 4
(70 GI (7 2 (7 3

From Guldberg and Waage's law, the velocity of the decomposition of steam will
be proportional to the product of the concentrations of each of the reacting mole-
cules. There are presumably three molecules of iron and four of steam. Hence,
the velocity of the decomposition of steam=&(7 3 Ci 4 ', and, similarly, the velocity
of the oxidation of hydrogen =h'C<C z . The condition of equilibrium when these
two velocities are equal must therefore be &C' 3 (7 1 4 =A;'C' 2 4 C'3. The condition of
equilibrium, however, is independent of the concentrations of the two solids ; and
hence, &C 3 niust be a constant number, say k ; and likewise, &'C 3 must be another
constant number, say & 2 . The condition of equilibrium can accordingly be written
Jfc 1 Ci 4 =fc2^'2 4 ' The concentrations of the two gases, hydrogen and steam, must be
proportional to their partial pressures p and p z respectively. Accordingly, the
preceding equation can be written :


rL = Constant


since the fourth root of a constant is itself constant. In an experiment by G. Preuner
(1904), 7 at 200, when the partial pressure of steam p l was 4'6 mm. of mercury,
that of hydrogen was 95*9. Hence, the value of the constant is nearly 0'048. In
another experiment at the same temperature, the partial pressure of hydrogen
Pi was 195'3, then that of steam p 2 must have been 0'048xl95*3=9'3 the
observed value was 97. The value of the constant at 440 was 0176 ; at 900,
0-69 ; at 1025, 0'78 ; and at 1150, 0'86, showing that thematic of steam : hydrogen
approaches unity with a rise of temperature.

EXAMPLES.- (1) If p v denotes the partial pressure of steam, p z that of hydrogen, and
p s that of oxygen, show that if k is a constant, then, for the reaction 2H 2 Ov^2H 2 -{-O 2 ,

(2) When barium peroxide is heated, it decomposes : 2BaO 2 ^2BaO + O 2 . Show that
for any given temperature, p=constant, where p denotes the partial pressure of oxygen.


1 I. Kant, Metaphysischen Anfangsgrunden dcr Naturwisscnschaften, 1786.

2 J. H. van't Hoff, Etudes de dynamique chimique, Amsterdam, 13, 1884.


J. H. Mathews and H. A. Curtis, Journ. Phys. Chem., 18. 161, 521, 1914.
J. Walker, Proc. Roy. Soc. Edin., 22. 22, 1898.
G. Bredig and M. von Bcrneok, .Zeit. phys. Chem., 31. 289, 1900.
G. Dyer and A. B. Dale, Proc. Chem. Soc,, 29. 55, 1913.

G. Preuner, Zeit. phys. Chem., 47. 385, 1904; H. St. C. Deville, Compt. Kend., 70. 1105,
1201, 1870 ; 71. 30, 1870 ; H. Debray, ib., 88. 1241, 1879.

11. The Chemical Properties of Hydrogen Peroxide

Solutions of hydrogen peroxide are not very stable, and readily decompose into
oxygen and water. Similar remarks apply to the anhydrous peroxide. If the
liquids are free from other substances they are moderately stable at ordinary
temperatures. J. W. Briihl l found that after anhydrous peroxide had been kept 50
days protected from atmospheric dust, it had lost only one-half per cent, of peroxide
by decomposition. According to R. Wolffenstein, aqueous solutions keep very well
if they are free from alkaline substances, salts of the heavy metals, and from particles
of alumina and silica. R. Bottger, M. Berthelot, and P. Sabatier found that the
presence of acids increases the stability of aqueous solutions. A 3 per cent, solu-
tion suffered no appreciable change after it had been kept for a year. The fact was
well known to L. J. Thenard, who considered that the acid combines chemically
with hydrogen peroxide. He said :

With phosphoric, sulphuric, hydrochloric, hydrofluoric, nitric, oxalic, citric, and acetic
acids hydrogen peroxide forms compounds in which it is less easily decomposable than when
alone. In these compounds, the acid was at first regarded as existing in a higher state of
oxidation. The comparatively weak carbonic and boracic acids do not give stability to
peroxide of hydrogen. . . . The evolution of oxygen gas from these mixtures takes place
less easily and more slowly than from the pure peroxide of hydrogen ; but when the acid
is neutralized by an alkali, the former facility of decomposition is restored. The greater
the quantity of acid mixed with the peroxide, the more does the affinity of the acid for
that compound interfere with its decomposition by elevation of temperature, or by contact
with most of the bodies mentioned below. If any of the acids just enumerated be added
to hydrogen peroxide which has begun to evolve gas, the escape of gas ceases ; it recom-
mences at a higher temperature, but the whole of the oxygen is not driven off, even by
half an hour's boiling. It is remarkable that although gold decomposes the pure peroxide
much more rapidly than bismuth does, yet the quantity of acid required to stop the action
of the gold is smaller than that which must be added to prevent the action of the bismuth.
Hydrogen peroxide brought into a state of effervescence by gold, palladium, or rhodium,
is restored to tranquillity by the addition of a single drop of dilute sulphuric acid.

L. J. Thenard also knew that alkaline solutions do not keep very well. G. Lemoine
attributes the retarding effects of acids to their affinity for water which counter-
acts the catalytic action of the water ; he attributes the accelerating effects of the
caustic alkalies to the cyclic formation and decomposition of alkali peroxides.
Hydrogen peroxide solutions corrode glass vessels faster than water, and the liquid
becomes alkaline. Hydrogen peroxide is for preference kept in paraffin or paraffin-
lined glass bottles, or in quartz-glass vessels. The rate of decomposition of solu-
tions of hydrogen peroxide prepared with ordinary tap-water is said by W. Clayton
to be fifty times the rate with highly purified water.

A little platinum black dropped into the solution may cause an explosion ; in
any case, it causes rapid decomposition. Similar remarks apply to finely divided
gold, silver, and similar metals, as well as to powdered manganese dioxide. The
action appears to be catalytic since the manganese dioxide, etc., remains at the
end of the action unchanged in composition. 2

J. L. Thenard's classical observations on the action of various substances on
eau oxygenee are worth quoting :

Substances which induce the evolution of oxygen without themselves undergoing any
alteration : A violent action occurs with charcoal (forming carbon dioxide), silver, gold,
platinum, palladium, rhodium, iridium, and osmium. The action is the more vigorous


the finer the state of subdivision of the metal. A moderate action occurs with mercury,
lead filings, powdered bismuth, and powdered manganese. The action is slight with
copper, nickel, cobalt, and cadmium. A violent reaction occurs with manganese dioxide,
manganese and cobalt sesquioxides, and lead monoxide. The reaction is moderate with
ferric, potassium, sodium, magnesium, and nickel hydroxides. The reaction is mild with
ferric, nickel, copper, bismuth and magnesium oxides ; and feeble with the magnetic oxide
of iron, and with uranium, titanium, cerium, and zinc oxides, and the hydrated dioxides
of calcium, strontium, and barium. The reaction is very feeble with sodium carbonate,
potassium hydrogen carbonate, manganous, zinc, ferrous, and copper sulphates ; with
potassium, sodium, barium, calcium, antimony, ammonium, and manganous chlorides ;
and with manganous, copper, mercurous, and silver nitrates. The fibrin of blood acts

Substances which induce the evolution of oxygen but at the same time give up their
own oxygen by reduction : -The oxides of platinum, gold, silver, and mercury are reduced
to the metallic state ; lead dioxide and red lead are reduced to lead monoxide. The action
is in all cases violent.

Substances which allow some of the oxygen of the peroxide to escape as a gas and them-
selves absorb the remainder of the gas to form oxides : Examples are selenium forms
selenic acid ; arsenic or arsenious oxide forms arsenic acid ; molybdenum, molybdic acid ;
tungsten, tungstic acid ; and chromium, chromic acid. The metals potassium and sodium
are violently oxidized ; zinc forms zinc oxide ; barium hydroxide forms barium dioxide ;
copper oxide forms a yellow peroxide ; manganic oxide forms manganese dioxide ; cobalt
and iron monoxides form sesquioxides. The sulphides of arsenic, molybdenum, antimony,
lead, iron, and copper are vigorously oxidized to sulphates ; bismuth and stannic sulphides
are slowly converted into sulphates ; mercury and silver sulphides are not oxidized ; and
barium iodide probably forms the iodate.

The following oxides take the whole of the oxygen they require from hydrogen peroxide
without liberating any gas sulphur dioxide forms the trioxide ; hydrosulphuric acid gives
water, sulphur, and a little sulphuric acid ; hydriodic acid forms iodine and water ; the
peroxides are precipitated from lime, strontia, or baryta water ; and stannous oxide forms
stannic oxide.

No action was observed with antimony ; tellurium ; tin ; iron ; alumina ; silica ;
tungstic acid ; chromium sesquioxide ; antimonious and antimonic oxides ; stannic oxide ;
sodium phosphate ; potassium, sodium, calcium, barium, or strontium sulphate ; alum ;
turbite ; potassium chlorate ; potassium, sodium, barium, strontium, or lead nitrate ;
zinc, stannic, or mercuric chloride ; white of egg liquid or coagulated ; glue ; and urea.

Hydrogen peroxide is not decomposed perceptibly faster with organic substances like
potassium oxalate or acetate, alcohol, camphor, olive oil, sandarac, woody fibre, starch,
gum, sugar, mannite, and indigo than when it is alone, but in some cases, the gas evolved
is mixed with carbon dioxide e.g. with starch or sugar.

J. H. Walton and D. 0. Jones 3 found that the metal salts which catalytically
decompose hydrogen peroxide in aqueous solutions, act similarly if amyl alcohol,
amyl acetate, isobutyl alcohol, or quinoline be substituted for water. The reaction
with manganese acetate in a solution of quinoline with 2 per cent, of water is
bimolecular, and unimolecular if the quinoline be saturated with water. A small
trace of some of the extremely finely divided metals colloidal platinum, colloidal
gold, etc. can accelerate the decomposition of an indefinitely large amount of the
peroxide. The action, though different, has been compared with that of yeast on
a solution of sugar, and these colloidal metal solutions have been styled inorganic
ferments. According to G. Bredig, a gram-atom of colloidal platinum diluted to
approximately 70 million litres, can distinctly accelerate the decomposition of more
than a million times this amount of hydrogen peroxide. The reaction in neutral
and acid solutions is unimolecular, and is irreversible and complete, H 2 2 =H 2 0-fO,
not 2H 2 2 =2H 2 0-|-02 ; with organic ferments, the reactions are not usually
complete. Under similar circumstances, in alkaline solutions, one gram-atom of
colloidal manganese diluted to 10,000,000 litres ; colloidal cobalt or copper to one
million litres ; and colloidal lead to 100,000 litres, can act in a similar way ; since
their action is more or less retarded or paralyzed by traces of certain other sub-
stances, so that the inorganic ferments are said to be poisoned by these agents. 4
The catalysis of hydrogen peroxide by colloidal platinum, and the poisoning of the
catalyst has been studied by G. Bredig and his co-workers, J. H. Kastle and A. S.
Loevenhart, E. H. Neilson and 0. H. Brown, etc. The following act as poisons
in retarding the activity of colloidal platinum : arsine, phosphine, phosphorus,


carbon disulphide, mercuric chloride, sulphide, or cyanide ; hydrocyanic acid ;
cyanogen iodide ; bromine ; iodine ; hydrogen sulphide ; sodium thiosulphate,
nitrate, and sulphite ; carbon monoxide ; aniline ; hydroxylamine ; hydrochloric
acid ; oxalic acid ; arsenious acid ; phosphorous acid ; nitrous acid ; hydrofluoric
acid ; amyl nitrite ; pyrogallol ; nitrobenzene ; and ammonium chloride and
fluoride. The decomposition is accelerated by hydrazine, dilute nitric acid, and
formic acid ; and it is not affected by potassium chlorate, ethyl alcohol, amyl
alcohol, ether, glycerol, turpentine, and chloroform. G. Phragmen studied the
effect of sodium phosphate and of the hydroxide on the decomposition of hydrogen

G. Bredig and W. Reinders investigated the influence of colloidal gold on the
decomposition of hydrogen peroxide in alkaline solutions, and the poisoning of the
catalytic agent by potassium chloride, sodium phosphate, potassium cyanide,
sodium sulphide, thiosulphate, and sulphite. Mercuric chloride stimulates the
activity of the catalyst probably because that salt is reduced to colloidal mercury,
which itself acts catalytically. In feebly alkaline solutions, the effect of 0*0003
rngrm. of colloidal gold is perceptible per c.c. of solution. G. Bredig and his co-
workers have investigated the action of colloidal palladium under similar conditions.
The catalytic agent is activated by hydrogen. Hydrogen cyanide, hydrogen
sulphide, arsine, iodine, and mercuric chloride act as poisons ; while carbon monoxide
acts first as a positive and then as a negative catalyst. G. A. Brossa investigated
the catalytic action of colloidal iridium ; F. Ageno, colloidal boron ; and G. Bredig
and A. Marck, colloidal manganese dioxide. C. Doelter investigated the effect of
a number of minerals ; G. Lemoine, the effect of wood charcoal ; and E. B. Spaer,
the effect of pressure on the decomposition of hydrogen peroxide.

The decomposition of hydrogen peroxide by blood, haemoglobin, animal or
plant extracts, etc., has been studied by A. Bechamp, G. Senter, etc. 5 F. L. Usher
and J. H. Priestley, A. Heffter, J. Dewitz, K. Togami, and E. J. Lesser 6 have studied
the catalysis of enzymes ; A. Bach, by yeast catalase ; H. van Laer, by diastase ;
A. Renard, by milk ; and J. J. Ford, by starch. In a general way, the agents
which retard the activity of colloidal platinum also retard the activity of proto-
plasmic catalysts, but not all those which retard the activity of the latter
interfere with the activity of the former.

Charcoal or magnesium mixed with a trace of manganese dioxide ignites
immediately in contact with hydrogen peroxide. With finely powdered iron
or lead, hydrogen peroxide remains quiescent, but if a trace of manganese
dioxide be present, the iron burns. A few drops of liquid hydrogen peroxide
on a piece of cotton wool will make the cotton inflame, although the peroxide
can be filtered through gun-cotton. Similar results are obtained with aqueous
solutions of hydrogen peroxide, but the action is much less vigorous. Rough
surfaces have a disturbing effect on the stability of hydrogen peroxide a
concentrated solution is decomposed when poured on a ground-glass surface.
W. Clayton (1916) considers that the chief factor in the decomposition of aqueous
solutions of hydrogen peroxide is colloidal organic matter ; he doubts if the nature
of the surface of the vessel is really so active as is generally supposed ; and he
further attributes the observed effects to variations in the amount of colloidal
organic matter which is present. The presence of small quantities of some sub-
stances 7 e.g. alcohol, glycerol, ether, naphthalene, sodium pyrophosphate, oxalic
acid, pyrogallol, acetanilide (1 : 2000) ; magnesium silicate ; etc.- act as preserva-

Online LibraryJoseph William MellorA comprehensive treatise on inorganic and theoretical chemistry (Volume 1) → online text (page 157 of 177)