Thermochemistry online

unless very strong potash is used, and it was therefore necessary,
on analyzing the solution, to determine not only the amount of
hydrochloric acid formed, but also that of the carbon dioxide
absorbed, so as to make the requisite correction in the calcula-
tion for the carbon dioxide which escaped absorption. On



240 COMPOUNDS OF NON-METALS

the complete decomposition of i gram-molecule of COCL,, and
the absorption of the whole of the gas formed, there is a heat-
evolution of 105,1750, from which we calculate in the usual
manner that the heat of formation of carbonyl chloride is
55,620 c.

To control the accuracy of these numbers, a second series
of determinations was carried out, in which carbonyl chloride
mixed with hydrogen was burned in oxygen in precisely the
same manner as in the preceding experiments with CC\ 4 and
C 2 C1 4 . According to these experiments the heat of formation
of carbonyl chloride should be 54,650 c, whilst the decomposi-
tion with potassium hydroxide gave the value 55,620 c. We
can therefore put the heat of formation of carbonvl chloride at

(c, o, a,) = 55,140 c.

Since the heat of formation of carbon monoxide is 2 9,000 c, we
obtain

(CO, 0,) = 26,140 c,

and this high thermal value explains the direct formation of
carbonyl chloride from carbon monoxide and chlorine.



D. COMPOUNDS OF CARBON WITH SULPHUR AND NITROGEN.

i. Carbon disulphide^ CS 2 . The heat of formation of
carbon disulphide is deduced from the heat of combustion
of the substance in oxygen. Together with the dioxides of
carbon and sulphur there is always formed a small amount of
sulphur trioxide, so that in the calorimetric experiments the
products of the combustion must be quantitatively analyzed.
Carbon disulphide in the form of vapour is passed into the
calorimeter, and from the measured thermal effect the heat oj
combustion of the gaseous substance at 20 can be calculated.
Assuming the combustion to be normal, that is to say, that the
products are exclusively composed of the dioxides of carbon
and sulphur, we find that

(CS 2 : O,) = 265,130 c.



HEAT OF FORMATION 241

From this we calculate in the usual manner that the heat of
formation of i gram-molecule of CS. 2 in the gaseous state is

((7, S. 2 ) = 26,010 c for gaseous CS^ at 20.

Since the heat of vaporization of i gram-molecule of carbon
disulphide is 6400 c, the heat of formation will consequently be

(C, -S' 2 ) = 19,610 c for liquid CS 2 .

The heat of formation is in all cases negative; but this
arises from the large amount of energy with which the carbon
must be supplied in order to bring about the conditions under
which it enters into its compounds. I shall deal with this
subject in a later chapter on the heat of formation of organic
substances. Carbon is known to unite directly with sulphur,
but only at a high temperature ; and this is also the case when
carbon combines with oxygen and with hydrogen.

2. Carlonyl sulphide. This compound was formed directly
from carbon monoxide and sulphur vapour, which combine
with ease when they are led together through a tube filled
with pumice and warmed. The compound was purified by
treatment with alcoholic potash, when it is converted into
ethylmonothiocarbonate of potassium, which, after crystalliza-
tion from absolute alcohol, was decomposed with hydrogen
chloride. The product was washed with water at o, dried, and
collected in a gasometer over mercury. On combustion in
oxygen it, similarly to carbon disulphide, forms a little sulphur
trioxide, the amount of which must of course be determined.
The heat of combustion was found to be

(COS: O 3 ) = 131,010 c.

This is almost exactly half of the heat of combustion of
i gram-molecule of CSo, for which we found 265, 130 c. From
the heat of combustion we can, in the usual manner, find the
heat of formation of i gram-molecule of COS, namely

(C, 0, S) = 37,030 c,

from which, finally, we can deduce the thermal effect on
T.P.C. K



242 COMPOUNDS OF NON-METALS

formation of carbonyl sulphide from carbon monoxide and
sulphur, namely

(CO, S) = 8030 c.

These values apply to rhombic sulphur and amorphous
carbon.

It is worthy of note that the heat of formation of carbonyl
sulphide lies about midway between the heats of formation of
carbon dioxide and of carbon disulphide, and similarly that
that of carbonyl chloride lies about midway between those
of carbon dioxide and of carbon tetrachloride. Thus we
have

(<9, C, O) = 96,960 c (O, C, O) = 96,960 c
(S, C, O) = 37,3c (C/ 2 , C, O) = 55,140
(S, C, S) = -26,010 (67 2 , C, C7 2 ) = 21,030.

In the first case the mean value is 35,475 c; in the second,
58,995 c. The explanation of this difference may possibly be
that a reaction takes place within the unsymmetrical molecule,
between sulphur and oxygen in the one case, and between
chlorine and oxygen in the other ; the former gives rise to an
increased heat of formation, the latter, on the contrary, to a
lower.

3. Cyanogen and hydrogen cyanide. The heats of formation
of these two carbon compounds are derived from their heats
of combustion, which are respectively 259,6200 and 158,6200
(see Part IV.). Calculating in the usual manner we find

(C 2 , -AQ = -65,7000
(ff,C,JV)=- 27,480.

The heats of formation are therefore strongly negative,
which is due to the amount of energy which must be supplied
to the carbon in order to bring about the condition under
which it enters into chemical compounds. On the other hand,
cyanogen and hydrogen combine with evolution of heat. From
the numbers above we calculate that

H z ) = 2(H, C, N) - (C* N,) = 10,740 c.



HEAT OF FORMATION 243

Thus the heat evolved is about one-quarter of that observed
in the action of i gram-molecule of chlorine upon i gram-
molecule of hydrogen (namely, 44,000 c).

In Chapter IX. which follows will be found tabulated the
numerical results of the whole of my researches on combina-
tions between the non-metals.



CHAPTER IX

COMPOUNDS OF THE NON-METALS. COMPARATIVE
TABLES OF THE NUMERICAL RESULTS

THE following tables contain the results of researches on com-
pounds of the non-metals arranged in the manner most conve-
nient for reference. The substances are arranged in groups in
the order of their valency, so that each group contains all the
values connected with that particular non-metal. But in order
to avoid repetition, the arrangement is, as a rule, based upon
the electro-positive non-metal of the compound. So that, for
example, all the compounds of sulphur, whether they contain
oxygen, hydrogen, or chlorine, will be found under the group
sulphur, similarly the oxygen, hydrogen, chlorine, and sulphur
compounds of carbon are placed in the carbon group.

All the thermal values quoted apply to reactions of the
constituents at a temperature of from 18 to 20 C., and at
constant pressure. Unless anything to the contrary is stated,
the state of aggregation is always that in which the substance
occurs under normal conditions at the temperature specified ;
so that bromine and water are referred to as liquids, iodine,
sulphur, and phosphorus, on the other hand, as solids.

In the formulae employed the reactions are always supposed
to take place between those constituents which are separated
by a comma ( , ) or by a colon ( : ), and in those proportions
which are represented by the formula. -The comma usually
indicates that the constituents enter into direct combination ;
the colon, on the contrary, that they decompose one another.
The sign Aq in the formulae represents a large amount of water,
and consequently indicates that the reaction in question is



HEAT OF FORMATION 245

heaf oft' ta r e Pla r ^ S ' Uti0n ; thUS (ffa < ^ si g" ifies *
heat of absorption of gaseous hydrogen chloride, but (H Cl Aa)

expresses the formation of an aqueous solution of hydr'ochlorfc
acid from the constituents hydrogen, chlorine, and water

Ihe atomic weights used for the non-metals will be 'found

* Page 45, and the thermal value expresses the number of

-that is to say, that amount of heat required to raise

urn .weight of water at ,8 through , C.-correspondin*

to that weight of the reacting substances which the formula

represents.



TABLE 18.

THERMAL EFFECT ON FORMATION OF COMPOUNDS OF
THE NON-METALS.

(a) Hydrogen and Hydrogen Peroxide.



Reaction.


Thermal effect.


Remarks.


/ D rr\


22,000 c


, The thermal effect is valid for


(Br, H}
(/, 'ff)
(0, H,)


8,440
6,040
+ 68,360


\ the reaction at constant pres-
sure, and for the constituents
and products in their normal


' **w


2,730


V state of aggregation at 18.


(C,Ill)
(C*, H*}


11,890
21,750
28,560


/ The heat of fusion of I gram-
molecule of H 2 O, according
to Regnault, is 1440 c, and


(C 2 , HI)


2,710


I the heat of vaporization is


(C 2 , //)


-47,770


/ 9660 c at 100.


(C , ff\ I


~ 5,310


Valid for liquid benzene.


(Cl, H}


12,510
2I,984 + 0-9/,


,, benzene vapour at 1 8.
Valid at temperature /, when


U?ff\


-605 + 0-9 / 1 botn the constituents and the
57,903 + i '6 / If P roduct s formed are assumed


[S, Jfy]


iUtf -f I*Q/ 1 t0 be in the state of S a s or



, Aq\

O, Aq}



HYDROGEN PEROXIDE.



45,3oo c

23,060

91,420



Formation and decomposition of
hydrogen peroxide iu aqueous
solution.



246



COMPOUNDS OF NON-METALS



(&) Oxygen.



Reaction.


Thermal effect.


Remarks.


(ff 0)


68,360 c


Product : liquid.


(CV 2 , 0)


- 17,930


gaseous.


(N,, 0)


-17,470


,, >


(N,0)


-21,575


,, 5


(C, 0)


+29,000


For amorphous carbon.


(C, 0,)


96,960


(Favre).


(S, 0.)


71,080


Product : gaseous.


(Se, 0,)


57,080


crystalline.


W O t )


- 8,125


| NO 2 completely dis-
\ sociated.


W, 0.)


2,650


N 2 O 4 non-dissociated.


(S, 3 )
(As,, 0,)


103,240
154,670


liquid,
solid.


(/ 5 )


45,030





(As,, 0.)


219,380


ii



(c) Chlorine.
:. GENERAL SUMMARY.



or, CD

(/, d)
(/, C7 3 )


22,000 C

5,830
21,490


Of these compounds, HCl and
C1 2 O are gases ; IC1 3 , SeCl 4 ,
TeCl 4 , PC1 5 , SbCl 3 , and BiCl 3


((9, (7/ 2 )

(.5%, C/ 2 )
(Se, Cl,}
(TV, C/ 4 )

(X c/1)

(^, C 1 /,)
(., C/,)

w CV 5 )

(*/, C/,)


-17,930

+ 14,260

22,150

46,160

77,380
75,300
104,990
71,380
91,390

104,870
90,630


are solids ; and the remaining
compounds are liquids at 18
to 20. The thermal values
are valid for the substances in
their normal state of aggrega-
tion at this temperature, and
for rhombic sulphur, amor-
phous selenium, metallic tel-
lurium, regular phosphorus,
and amorphous carbon.


(C, C7 4 )


28,230


Product : liquid.




21,030


,, gaseous.


// /-y \ J


6,000


,, liquid.


\i/2, ^*4/ |


- 1,150


gaseous.


2. HYDROCHLORIC ACID, HCl.


(H, Cl)


22,000 C


Product: gaseous.


(If, Cl, Aq)


39,3 J 5


,, aqueous solution.


(HCl, Aq}


I7,3i5


Heat of absorption.


(NaOHAq, HClAq)




,, neutralization.



HEAT OF FORMATION



247



Reaction.


Thermal effect.


Remarks.


3. HYPOCHLOROUS ACID, HC1O.


(Ck, 0)
(C1 2 , 0, Aq)
(Cl,0, Aq}
(H, Cl, 0, Ay)
(NaOHAq, HClOAq)


-I7,930C
- 8,490
+ 9,440
29,930
9,980


Product : gaseous.
,, aqueous solution.
Heat of absorption.
Product: HClOAq.
Heat of neutralization.


4. CHLORIC ACID, HC1O 3 .


(Ck, 5 , Aq)
(H, Cl, 3 , Ay)
(HClOAq, 2 )
(HClAq, 3 )
(KOHAq, HClO.Aq}


20,480 c
+ 23,940
~ 5,990
-15.380
+ 13,760


Product : Cl 2 O 5 Aq.
HC10,Aq.
\ Formation of HC1O 3 by oxida-
/ tion of HClOAq or HClAq.
Heat of neutralization.


5. POTASSIUM CHLORATE, KC1O 3 .


(K, Cl, 3 )
(KCl, 3 )

(KCIO Z , Aq)

(K, Cl, 3 , Aq}
(KClOAq, O 2 )
(KClAq, 3 )


95,860 c

- 9,75
10,040
+85,820
2,210
-15,370


\ KC1O 3 formed from the elements
j and by oxidation of KC1.
Heat of solution.
Aqueous solution.
| Oxidation of KC1O or KC1 in
/ aqueous solution.


6. OXIDATION CONSTANTS.


2(ff, Cl, Aq} - (H^ 0}
(H,Cl,Aq)-(ff,Cl,0,Aq)
(ff,ClAq)-(H,Cl,O z Aq)
(C/ Aq)


10,270 c
9,38o
i5,38o
4,870


Oxidation by chlorine and water.
HC1 and HC1O.
HC1 and HClO a .
Heat of absorptiou.


(d) Bromine.


I. HYDROBROMIC ACID, HBr.


(H, Br)

(//, Br, Aq}
(HBr, Aq}
(NaOHAq, HBrAq)


8,440 c

28,380

19,940

13,750


Gaseous HBr ) formed from
Solution of HBr/liquid bromine.
Heat of absorption.
Heat of neutralization.


2. HYPOBROMOUS ACID, HBrO.


(Br 0, Aq}
(H, Br, 0, Aq)


~~ I 5'?-?>3 C 11 Product: aqueous solution.
+26,682 \)


3. BROMIC ACID, HBrO 3 .


(Br 2 , O & , Aq)
(H, Br, 3 , Aq)
(HBrAq, 3 )
(NaOHAq, HBrOzAq}


-43,520 c
+ 12,420
-15,960
I3J80


J Product : aqueous solution.

Oxidation of HBrAq.
Heat of neutralization.



COMPOUNDS OF NON-METALS



Reaction.


Thermal effect.


Remarks.


4. POTASSIUM BROMATE, KBrO 3 .


(K Br, 0,)

(KBr, O 3 )


84,060 c

1 1,250


Product : cryst. KBrO 3 .


(KBrO 3 , Aq)


9,760


Heat of solution.


(K, Br, 3 , Aq)


+ 74,300


Formation in aqueous solution.


(KBrAq, 3 )


-15,930


Oxidation of a solution of KBr.


5. OXIDATION CONSTANTS.


2(ff, Br, Aq} - (ff t , 0)


1 1, 600 C


Oxidation with bromine and water.


2(ff, BrAq) - (/y 2 , O)


-12,680


,, bromine water.


(Br z , Aq)


+ i, 080


Heat of solution.


(Brgas, Aq}
(Brgas) - (Brjiq.)


+ 7,643
+ 6,560


Absorption of bromine gas.
Difference in energy content at 19.


(e) Iodine.


i. HYDRIODIC ACID, HI.


(H, 1}


6,040 c


Product : gaseous.


(H, I, Aq)


+13^70


,, aqueous solution.


(HI, Aq}
(NaOHAq, HIAq}


19,210
13,680


Heat of absorption.
,, neutralization.


2. IODIC ACID, HIO 3 .


(/ gj o & )


45,030 c


Product : I 2 O 5 .


(H, I, 3 )


57,960
47,570


HI0 3 .
2HIO,.


( lk fojAy)


43,240
55,800


> ,, aqueous solution.


(7 2 6> 5 ,' 7/!b)


2,540


Heat of hydration.


(7 2 G> 5 , Ay)


- 1,790


}lleat of solution.


(777Oj, Aq)


- 2,170




(HIAq, 3 )
(777, O 3 )


+42,630

64,000


\ Oxidation of HIAq to HIO 3 Aq.
/ and of gaseous HI to solid HIO,.


3. POTASSIUM IODATE, KIO S .


(K, I, O 3 )
(KI, 3 )


124,490 c

44,360


1 Product : solid.


(KIO Z , Aq}


- 6,780


Heat of solution.


(K, 7, 3 , Ay)
(KIAq, 0,)


117,710
42,690


> Product : aqueous solution.


(KOHAq, HIO^Aq)


13,810


Heat of neutralization.


4. PERIODIC ACID, H 5 IO 6 .


(7/ fi , 7, 6 )


185,780 c


Product : crystalline.


(7/ 5 ' 5 7, 0., .4?)


184,400


,, aqueous solution.


(7/ 8 70 6 , ,4?)


- 1,380


Heat of solution.


(77, I^O^Aq}


27,000
47,680


> Product : aqueous solution.


(HIAq, <9 4 )


34,510


Oxidation of HI solution.


(KOHAq, HJO^Aq}


5,150


"I Heat of neutralization (sea


(zKOHAq, HJO^Aq}


26,590


/ p. 104).



HEAT OF FORMATION



249



Reaction.


Thermal effect.


Remarks.


5. CHLORIDES OF IODINE, ICl and IC1 3 .


(/ C!)


5,830 c


Product : liquid ICl.


(/, C1 3 )


21,490


solid IC1 3 .


(ICl, Cl,)


15,660


ici 3


(Itfas) - (I^olid)


10,900


Difference in energy content at 19 .


(/) Sulphur, Rhombic.


i. HYDROGEN SULPHIDE, H 2 S.


(#"2, -5)


2730 c


Product : gaseous.


(If,, S, Aq)


7290


,, aqueous solution.


(H,S, Aq)


4560


Heat of absorption.


2. SULPHUR DIOXIDE, SO 2 .


(S, 0,)


71,080 c


For monoclinic sulphur 71,720 c.


[S, O,]


77,280


Product : liquid SO 2 .


(S, O,, Aq)


78,780


,, aqueous solution.


(SOtgus) (SO,liq.)


6,2OO


Heat of liquefaction at 19.


(SO,, Aq)


7,700


,, absorption.


[SO,, Aq]


1,500


Solution of liquid SO 2 in water.


(2NaOHAq, SO,Aq)


28,970


Heat of neutralization.


3. SULPHURIC ACID, H 2 SO 4 .


(S, 3 )

(SO,, O)


103,240 c

32,160


Product : liquid anhydride.
Oxidation of SO 2 to SO g .


(If,, S,, Oj)


298,860


Product : liquid H 2 S 2 O 7 .


(2S0 3 , Jf,0)


24,020


Heat of hydration.


(H,, S, 0<)


192,920




(S, 3 , H,0)


124,560


Formation of liquid H 2 SO 4 from


(SO 3 , H,O)
(SO,, O, U,O)


21,320

53,480


the constituents specified.


(If,, SO,, 0,)


121,840




(S, 3 , Aq)


142,410


1 Formation of a solution of sul-


(SO,, O, Aq)
(SO,Aq, O)
(If,, S, O 4 , Aq)


71,330
63,630
210,770


phuric acid from the consti-
tuents specified.


(SO 2 , Aq)


39,170


Heat of solution of the anhydride


(ff,S,0,, Aq)


54,320


and acids in 1600 mol. H 2 O.


(Jf,S0 4 , Aq)
(2NaOHAq, S0 3 Aq)


17,850

31,380


Heat of neutralization.


4. THIOSULPHURIC ACID, H 2 S 2 O,.


(S,, 2 , Aq)
(H,, S,, 3 , Aq)
(SO,, S, Aq)
(SO,Aq, S)
(Na,, S,, 3 , $H,0)


69,470 c

137,830

1,610

- 9,3 10
265,070


| Formation in aqueous solution.

\ Formation from sulphurous acid
/ and sulphur.
Product : Na 2 S 2 O 3 + 5H,O.



250



COMPOUNDS OF NON-METALS



Reaction.


Thermal effect.


Remarks.


5. DITHIONIC ACID, H 2 S 2 O 6 .


(S 2 , O it Aq)
(H v S 9 , O s , Aq)


211,080 c

279,440


> Formation of aqueous solution.


(2S0 9 , 0, Aq)


68,920


I Formation by oxidation of SO 2


(2S0 2 Aq, 0)


53,520


f or SO 2 Aq.


(SO z Aq, S0 2 Aq)


10,110


f From sulphuric and sulphurous
[ acids.


(KnSO SO )


O




(K\, S 9 ', O 6 )


415.720


Product : solid K 2 S 2 O 6 .


(A' 2 S 2 O 6 , Aq)


13,010


Heat of solution.


(2KOHAq, S 2 5 Aq)


+ 27,070


,, neutralization.


6. TETRATHIONIC ACID, H 2 S 4 O 6 .


(S t , 0>, Aq)
(ff 2 , S 4t 6 , Aq)


192,430 c
260,790


> Formation in aqueous solution.




- 18,650
53,490


From dithionic acid and sulphur.
By oxidation of thiosulphuric acid.


7. SULPHUR CHLORIDE AND SULPHURYL CHLORIDE.


(S 2 , C7 2 )


14,260 c


Direct formation.


(S 2 a 2 , 2 s 2 )

(S, O 2 , Cli)


- I, 660
89,780


Solution of S in S 2 C1 2 .
Formation from the elements.


(SO,, Cl t )


18,700


SO 2 andCl 2 .


(g) Selenium, Amorphous.


I. CHLORIDES OF SELENIUM, S 2 C1 2 and SeCl 4 .


(Se,Cl 4 )


22,1500

46,160


> Direct formation.




70,170


Product : 2SeCl 4 .


(SeCl 4 1 Aq)


30,370


Heat of solution.


2. SELENIOUS ACID, SeO 2 .


(Se, 2 )


57,080 c


Product : cryst. SeO 2 .


(Se, O 2 , Aq)


56,160


,, aqueous solution.


(SeO 2 , Aq)


920


Heat of solution.


(Na 2 OAq, SeO^Aq)


27,020


,, neutralization.


3. SELENIC ACID, H 2 SeO 4 .


(Se, 3 , Aq)


76,660 c


Direct formation in solution.


(Se0 2 , 0, Aq)


19,580
20,500


| Oxidation of SeO 2 and SeO 2 Aq.


(H v Se, 'o t , Aq)
(ff 2 Se0 4 , Aq)


145,020

16,800


Product: H 2 SeO 4 Aq.
( Heat of solution of liquid H 2 SeO 4
\ (MetznerK


(S?,O e H\0)
(Na,OAq, Se0 3 Aq)


128,220

59,860
30,390


1 Product : liquid H 2 SeO 4 .
Heat of neutralization.



HEAT OF FORMATION



251



(K) Tellurium, Metallic.



Reaction.


Thermal effect.


Remarks.


i. TELLURIC CHLORIDE, TeCl 4 .


(Te y Cl,)


77,380 c


Direct formation.


(TeCl \Aq)


20,340


Heat of solution.


2. TELLUROUS ACID, H 2 T1O 3 .


(7>, 2t H 2 O) 77,i8oc From tellurium, oxygen, and water.


3. TELLURIC ACID, H 2 T1O 4 .


<7>, 3 , Aq)


98, 380 c


Direct formation in solution.


(H 2 Te0 3) 0, Aq)


21,200


By oxidation of tellurous acid.


(f) Nitrogen.


i. AMMONIA, NH 3 .


(N, 7/ 3 )


11,890


Direct formation.


(N, // 3 , Aq)


2O,32O


,, ,, in solution.


(.V//3, Aq)


8,430


Heat of absorption.


(NH^ HCl)
(NH Z , HBr)
(NH 3 , HI)
(NH Z , HSH)


41,900

45,020
43,460
22,440


ICryst. compounds : e.g. NH 4 C1
formed from the gaseous con-
stituents NH 3 and HCl.


(N, 77 4 , Cl)


75,790




(N, 7/ 4 , Br)


65,35




(N, // 4 , /)


49,3io


Formation of salts from their


(N, 77 5 , S)


37,060


' elements.


(yV 2 , 77 4 , 2 )


64,950




(N 77 4 , <9 3 )


88,060




(NH 3 Aq, HClAq)
(NH-iAq, HSHAq)


12,270
6,190


\ Heat of neutralization.


2. HYDROXYLAMINE, NOH 3 .


W H 3 , 0, Aq)


24,290 c


Direct formation in solution.


(NH z Aq, O)


3,970


By oxidation of NH 3 Aq.


(N, 0, // 4 , Cl)


76,510


Product : NOH 3 . HCl.


(NOH 4 Cl, Aq)


- 3,650
- 960


| Heat of solution.


(NOH^Aq, HClAq)
(2NOH 3 Aq, SO z Aq)


+ 9,260

21,580


\ ,, neutralization.


3. NITROUS OXIDE, N 2 O.


W, 0)

(NO, N)


-i 7,470 c

+ 3,885


Direct formation.
Formation from NO and N.


(N t O t 2lf 2 0)


-30,930


Product : NH 4 NO a .



252



COMPOUNDS OF NON-METALS



Reaction.


Thermal effect.


Remarks.



4. NITRIC OXIDE, NO.



(N, 0)

: o)



-21, 575
-25,410



Direct formation.
Product : 2NO.



5. NITROUS ACID, HNO 2 .



(A\, 3 , Aq)
(H, N, 2 , Aq)

(2N0 2 , O, Aq)
(ff, NO, O, Aq)

(N z , 2// 2 6>)



(#0, O)



- 6,820 c

+3o,77o

+36,330

+52,345

+71,770



Direct formation in solution.

Formation from NO.
Product : NH 4 NO 2 .



6. NITROGEN DIOXIDE, NO 2 .

+if *4D C \\ Product coni P letel y dissociated.
7. NITROGEN TETROXIDE, N 2 O 4 .



(N,, 4 )


- 2,650 c


Heat of formation without dis-


(2.NO, 2 )


+40,500


^ sociation of N 2 O 4 .


(N^Ov Aq)


14,150


Heat of absorption.


(NO,, NO Z )


13,600


N 2 O 4 formed Irom 2NO 2 .


8. NITRIC ACID, NHO 3 .


(H, N, 3 )


41,610 c


Direct formation, product liquid.


(H, N, 3 , Aq)


49,090


,, ,, in solution.


(ffNO z , Aq) 7,48o


Heat of solution.


(HN0 2 Aq, 0)


18,320


By oxidation of a solution of
\ HNO 2 .


(H, NO, 0,, Aq)


70,665


Formation of a solution of nitric


(ff, NO 2 , O, Aq)


57,215


acid from NO, NO 2 , and N 2 O 4


(7/ 2 , N Z 4 , 2 , Aq)


100,830


respectively.


(ff, NO, On)


63,185


Formation of nitric acid from


(H, NO Z , 0)


49,735


NO, NO 2 , and N 2 O 4 respec-


(ff,, N Z 4 , 2 )


85,870


tively.


(N,, O s , Aq)


29,820




(N*O, 4 , Aq)


47,560


Formation of N 2 O 5 Aq from N 2 ,


(2NO, O 3 , Aq)


72,970


N 2 O, 2NO, 2NO 2 , and N 2 O 4


(2NO 2 , O, Aq)


46,070


respectively.


(JV 2 O 4 , O, Aq)


32,470




(NaOffAq, ffNO 3 Aq)


13,680


Heat of neutralization .


9. CYANOGEN AND HYDROGEN CYANIDE, C 2 N 2 and HCN.


(ffl C, V)gas


65,700 c
-27,480


Product : gaseous.


(ff * C.N)


+ 10,740


2HCN.


(f/CN^Aq)


6,100


Heat of absorption.


(ff, C, N, Aq)


-21,380




(NaOffAq, HCNAq)


+ 2; 7 70


,, neutralization.



HEAT OF FORMATION
(k) Phosphorus, Regular.



253



Reaction.


Thermal effect.


Remarks.


i. CHLORIDES AND OXYCHLORIDES.


(P, C1 3 )


75.300 C


[Direct formation from the


(P, C7 5 )
(P, C1 3 , 0)


104,990
145,960


elements.


(PCI,, Cl,)


29,690


\ PC1 5 and POC1 3 formed from


(PCI,, 0)


70,660


/ PC1 3 .


(PCI, : Aq)


65,140




(PCI, I Aq)


123,440


Heat of solution.


(FOCI, : Aq)


72,190




2. HYPOPHOSPHOROUS ACID, H 3 PO 2 .


(H 3 , P, 0,) |


139,970 c
137,660


Cryst. acid.
Liquid acid.


(H 3 , P, 2 , Aq)


139,800


Aqueous solution.


(H,PO,, Aq) |


+2,140


Heat of solution of the cryst. acid.
liquid


(P 2 , O, $H 2 O)


74,860


Product : cryst. acid.


(P 2 , 0, Aq}


74,520


,, aqueous solution.


(NaOH, H 3 PO^Aq)


15,160


Heat of neutralization.


3. PHOSPHOROUS ACID, H 3 PO 3 .


r


227,700 c


Cryst. acid.


' 3> ' 3 ' (


224,630


Liquid acid.


(H 3 , P, O,, Aq)
(H 3 PO,, Aq) |


227,570
- 130
+2,940


Aqueous solution.
Heat of solution of the cryst. acid.
liquid


(/> 2 , O 3 , 3// 2 0)


250,320


Product: cryst. acid.


(P 2t 3 , Aq)


250,060


,, aqueous solution.


(2NaOH, H 3 P0 3 Aq)


28,450


Heat of neutralization.


4. PHOSPHORIC ACID, H 3 PO 4 .


k> \

(ff P, 4 , Aq)

1 TT Z>/~1 A \ 1


302,600 c
300,080

305,290
2,690


Cryst. acid.
Liquid acid.
Aqueous solution.
Heat of solution of the cryst. acid.


\"z* t/4, Aq)


5,210


,, liquid ,,


(A, oj


369,900


Anhydride.


(P 2 , O & , 3J7 2 <9)


400,120


Cryst. acid.


(A, O s , Aq)


405,500
34,030


Aqueous solution.
Heat of neutralization.



(As, C1 3 )



(/) Arsenic.
I. ARSENIOUS CHLORIDE, AsCl 3 .

7 I ,39 c I Direct formation.
Heat of solution.



254



COMPOUNDS OF NON-METALS



Reaction.


Thermal effect.


Remarks.



(As,, 3 )
(As,, 3 , Aq)
(As,0 3 , Ay)
(Na,OAq, As,O 3 Aq)



(As,, O s )
(As,, & ,
(As,O s , 3// 2 G>)
(As,, O,, Aq)
(ff 3 , As, 0<)
(As,0 3 , O,)
(As,O 3 Aq, O,)
(As,0 & , Aq)
** Aq)
H*



2. ARSENIOUS OXIDE, As 2 O 3 .

154,670 c
147,120



- 7,55o



Anhydride.
Aqueous solution.
Heat of solution.
,, neutralization.



3. ARSENIC ACID, H 3 AsO 4 .