What is the heat of combustion of 1 kg carbon dioxide w/ magnesium?

[James Essig]

TL;DR

I am trying to find out the heat of combustion of one kilogram of carbon dioxide with magnesium. I am looking for results for stochiometric conditions of these two reactants.

I am trying to find out the heat of combustion of one kilogram of carbon dioxide with magnesium. I am looking for results for stochiometric conditions of these two reactants.

I have found the following equation online

2 Mg(s) + CO2 ---> 2 MgO(s) + C(s) yields a standard enthalpy of --810.1 kJ/mol.

I would think that the C(s) is in its standard state and thus has a standard enthalpy of formation of zero joules/mol. Thus, I would tend to believe that the standard enthalpy of formation of 2 MgO(s) from the precursor magnesium and carbon dioxide is --810.1 kJ/mol.

 

[Lord Jestocost]

You must clearly distinguish between the standard molar reaction enthalpy, Δ_rH°, and the standard molar enthalpy of formation (or standard molar heat of formation), Δ_fH°.

Δ_rH° = -810.1 kJ/mol is the standard molar reaction enthalpy for the reaction 2Mg(s) + CO₂ ---> 2MgO(s) + C(s) .

The standard molar enthalpy of formation of a compound is the heat change accompanying the formation of one mole of compound from the elements at standard state.

For the standard molar enthalpy of formation of MgO(s) one has Δ_fH° = -601.7 kJ/mol for the formation reaction Mg(s) + 1/2O₂(g) ---> MgO(s).

 

[James Essig]

Thanks for your reply Lord Jestocost. Now I understand the reaction.