CO2 partial pressure and the enthalpy and thermodynamic efficiency of the oxidation of nitrite by Nitrobacter

Abstract The heat of reaction of the oxidation of nitrite by Nitrobacter was determined at different partial pressures of CO 2 . Its value decreases from the theoretical value of −24.6 kcal × mole −1 to −18.5 kcal·mole −1 , and levels at this value, as pCO 2 is increased from 0 to 10 vol% CO 2 at atmospheric pressure. The cell-free fixation of CO 2 depends on pCO 2 in an identical manner and is the mechanism responsible for the observed decrease in the apparent enthalpy. The overall thermodynamic efficiency of the nitrite oxidation can be calculated from two determinations of heats of reaction. This value is 34%.