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Recently I stumbled across a book that describes enthalpy change with temperature, specifically for a product of combustion process (e.g. CO as a result of solid carbon combustion). The book says that enthalpy of formation at $298$ K is $-110.5~\rm\frac{kJ}{mol}$, meaning that this is the amount of energy that gets released during combustion. But in a very next paragraph there are two opposite calculation for enthalpy at 2000K: one says it is $-53~\rm\frac{kJ}{mol}$ (less energy get released during combustion), and the other it is $+167~\rm\frac{kJ}{mol}$ (the energy must be brought into system)?

Can you please clarify which number is correct and does energy goes out or into the system?

M.A.R.
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Marin
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  • Well, perhaps you could summarize the 'two opposite calculations' to give us a hint about them and why they might be different? – Jon Custer Jan 28 '16 at 14:05
  • What it says is that the enthalpy at 2000 K (value of enthalpy in the book: -53 kJ/mol or +167 kJ/mol?) is the enthalpy of formation at 298 K (value = -110 kJ/mol) + change in enthalpy from 298 K to the 2000K (value = 57 kJ/mol). My guess is that authors ment this is enthalpy for a case where CO2 had to be first produced through the combustion at referent temperature 298 K (resulting in negative enthalpy of -110 kJ/mol) and then heated to 2000 K by adding 57 kJ/mol extra energy from enviroment. Resulting -167 kJ/mol would be just an error and -53 kJ is the right value. Does it sound ok? – Marin Jan 28 '16 at 15:13

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