Microscale Gas Chemistry
Carbon Monoxide Information

A. Appearance
     Carbon monoxide is a colorless, odorless and tasteless gas formed from the incomplete combustion of carbon.

C(s) + 1/2 O2(g) ---> CO(g)  DH = -110.5 kJ DS =  +89.4 J/K

Carbon monoxide is negligibly soluble in water.  It is flammable in air and burns with a characteristic blue flame to produce carbon dioxide:

CO(g) + 1/2 O2(g) ---> CO2(g) DH = -283.0 kJ DS =  -86.5 J/K

 The disproportionation equilibrium between CO(g) and C(s) and CO2(g) exists at all temperatures but is kinetically slow except at temperatures between 400 - 700 oC:

2 CO(g) ---> C(s) + CO2(g) DH = -172.5 kJ DS = -175.9 J/K

The forward reaction is not favored by entropy and at temperatures above 981 K (708 oC) the reaction shifts to the left and CO-formation is thermodynamically spontaneous.  An important industrial method for CO production utilizes this equilibrium; CO2 is passed over charcoal heated to redness.
 

B. Physical Properties of CO

Molecular mass:  28.0104 g/mol
melting point   -205.1 oC
boiling point   -191.5 oC


C. History
     Carbon monoxide was first isolated by Joseph Priestley in the 1770s.

D. Natural Abundance
     Carbon monoxide is produced whenever combustion of a carbonaceous material occurs with insufficient oxygen.
 

E. Industrial Production
     Pure carbon monoxide is produced by passing CO2(g) over charcoal heated to redness:

C(s) + CO2(g) ---> 2 CO(g)   DH = +172.5 kJ DS = +175.9 J/K

The disproportionation equilibrium between CO(g) and C(s) and CO2(g) exists at all temperatures but is kinetically slow except at temperatures between 400 - 700 oC.  The forward reaction is favored by entropy and at temperatures above 981 K (708 oC) the reaction shifts to the right and CO-formation is thermodynamically spontaneous.  At 1000 oC, the product mixture is 99% CO(g).

     Mixtures of CO(g) with other gases are produced by passing air over red hot coke C(s).  Because air is used, the resulting mixture is 70% N2(g) and about 25% CO(g):

2 C(s) + O2(g) ---> CO(g)   DH = -221.0 kJ DS = -179.4 J/K

 Steam can also be blown over red hot coke to produce mixtures of H2(g) and CO(g).  This mixture is called 'water-gas':

C(s) + H2O(g) ---> H2(g) + CO(g)   DH = +131.3 kJ DS = +133.7 J/K





F. Industrial Uses
     Carbon monoxide mixtures such as water-gas is used as a gaseous fuel.  Gaseous fuels are much easier to transport than solid or liquid fuels.  Gaseous fuels can be transported great distances through pipelines.
 

G. Gas Density of CO
     The density of CO(g) is 1.1449 g/L at 25 oC and 1 atm which is 3% lower than that of air.
 

H. Gas Solubility of CO
     Carbon monoxide is almost insoluble in water.  Only 0.00270 g CO dissolve per 100 mL H2O at 20 oC
 
 

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