Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

56 OXIDES.

reaction studied. In the synthesis of sulphuric anhydride this has been found

to be practically true; and it is therefore possible, when the analysis of the

equilibrium mixture at a given temperature is known, to compute the com-

position of the equilibrium mixture at any other temperature. The equi-

librium-constants, as above defined, for the sulphuric acid contact-process

have been found to be as follows:

(.

528°

579

627

680

K.

645. X10^2


646. X10^2
     31.6 X10^2
     8.93 X10J

t.

727

789

832

897

K.

2.82 X10^2

0.794X10^2

0.357X10^2

0.123X10^2

In accordance with the positive heat of reaction, Q = 21,700 calories, a

rapid diminution in the value of K is observed.

The practical application of the theory in the manufacture of sulphuric acid

is shown by the following yields calculated for various mixtures at different

temperatures:

Composition of Reacting Mixtures.

SO,

66.67

14.00

2.00

o 3

33.33

86.00

98.00

Yield of SO 3 at

400°

98.1

99.8

99.8

500°

91.3

97.9

98.2

700°

51.5

69.8

VI.2

900°

16.0

24.4

25.6

It is, therefore, more important that the process should be carried out at a
relatively low temperature than that an excess of oxygen should be employed.
On the other hand, the temperature cannot be made too low, as then the rate
at which the reaction takes place, even in the presence of a catalyzer, becomes
too small.
The so-called "blast-furnace equilibrium," 2 CO + 02 <=± 2 CO 2 , is displaced
with increase of temperature, and the reaction proceeds more in the direction
from right to left, because here again the heat of reaction is positive; cf. No. 1.

OXIDES.

27. Liquid Sulphur Dioxide.
    Sulphur dioxide is prepared technically by burning either sulphur or
    pyrite. On a small scale, it is obtained by the reduction of concentrated
    sulphuric acid, or its anhydride, which when hot has a strong oxidizing power:
    SO 3 + Cu = SO2 + CuO.

The reduction with copper takes place also to a slight extent, according to the
equation:
SO 3 + 4 Cu = CuS -I- 3 CuO.