This reaction is called carbon monoxide poisoning. Carbon monoxide has a great affinity to hemoglobin relative to oxygen, so it spontaneously combines with hemoglobin. The overall balanced reaction is:
[tex] O_{2}Hb + CO = COHb + O_{2} [/tex]
There is a 1:1 molar ratio from oxygenated hemoglobin to each of the products. Thus, there is also 4.5 mol of released oxygen and 4.5 mol of hemoglobin bound to carbon monoxide.
