The Equilibrium 2CO = CO₂ + C

The reversibility of this reaction was discovered by Deville in 1864, and its study receives renewed interest in view of recent developments in the theory of the combustion of carbon in oxygen to which reference has already been made. By circulating carbon dioxide continuously over purified wood charcoal packed in a porcelain tube heated to a high temperature, and subsequently analysing the gas when equilibrium had been reached, Rhead and Wheeler obtained the following results:

Temperature, Absolute.	Temperature, °C.	100 C1, i.e. CO per cent, by Volume.	100 C2, i.e. CO2 per cent, by Volume.	K.
1073	800	86.15	13.85	18.76
1123	850	93.13	6.87	18.75
1173	900	96.63	3.37	18.74
1223	950	98.33	1.67	18.74
1273	1000	99.15	0.85	18.74
1323	1050	99.55	0.45	18.74
1373	1100	99.75	0.25	18.75

These results refer to atmospheric pressure, and K is calculated from a modification of Le Chatelier's formula, namely:



where T is the absolute temperature, and C₁ and C₂ are as defined in the table. P in this case is unity so that log_eP disappears.

No matter how high the temperature, theory demands the existence of a small but definite quantity of carbon dioxide in equilibrium with the monoxide.

A study of the velocity of reduction of carbon dioxide by carbon at 850° C. shows that the reaction is monomolecular, and the same is true for the reverse reaction, namely the decomposition of carbon monoxide, which, however, proceeds 166 times more slowly. Undoubtedly, therefore, the reactions are essentially surface phenomena, the rates varying directly with the partial pressure of the gas in either case. Since the decomposition of carbon monoxide is accompanied by a reduction in volume, increase of pressure should facilitate the reaction at constant temperature, and shift the equilibrium

2CO ⇔ CO₂ + C

in the direction left to right. That such is the case is shown by the following data:

Temperature, °C.	Pressure in Atmospheres.	CO2 %	CO %
800	1.23	16.12	83.88
	2.10	22.85	77.15
	3.05	28.40	71.60
900	0.65	2.17	97.80
	2.90	9.05	90.95
1000	0.66	0.65	99.35
	0.93	0.72	99.28
	2.02	1.63	98.37
	3.08	2.77	97.23
	3.78	3.17	96.83
1100	1.33	0.35	99.65
	3.64	0.92	99.08