Note 25 — Chapter IX · COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN

A molecular weight of this gas, or 2 volumes CO (28 grams), on combustion (forming CO2) gives out 68,000 heat units (Thomsen 67,960 calories). A molecular weight of hydrogen, H2 (or 2 volumes), develops on burning into liquid water 69,000 heat units (according to Thomsen 68,300), but if it forms aqueous vapour 58,000 heat units. Charcoal, resolving itself by combustion into the molecular quantity of CO2 (2 volumes), develops 97,000 heat units. From the data furnished by these exothermal reactions it follows: (1) that the oxidation of charcoal into carbonic oxide develops 29,000 heat units; (2) that the reaction C + CO2 = 2CO absorbs 39,000 heat units; (3) C + H2O = H2 + CO absorbs (if the water be in a state of vapour) 29,000 calories, but if the water be liquid 40,000 calories (almost as much as C + CO2); (4) C + H2O = CO2 + 2H2 absorbs (if the water be in a state of vapour) 19,000 heat units; (5) the reaction CO + H2O = CO2 + H2 develops 10,000 heat units if the water be in the state of vapour; and (6) the decomposition expressed by the equation 2CO = C + CO2 (Note 24 bis) is accompanied by the evolution of 39,000 units of heat.

Hence it follows that 2 volumes of CO or H₂ burning into CO₂ or H₂O develop almost the same amount of heat, just as also the heat effects corresponding with the equations

C + H₂O = CO + H₂ C + CO₂ = CO + CO

are nearly equal.