Wanted a second opinion on a value I\'m using for the heat of combustion of magn

Question

Wanted a second opinion on a value I'm using for the heat of combustion of magnesium. I'm using the standard enthalpy of formation for MgO (-601.6 kJ/mol). I need the value for the heat of combustion of magnesium and I thought the standard enthalpy of formation for MgO would be equivalent. Is this true and if not what is the heat of combustion of magnesium (preferably per mole)? Wanted a second opinion on a value I'm using for the heat of combustion of magnesium. I'm using the standard enthalpy of formation for MgO (-601.6 kJ/mol). I need the value for the heat of combustion of magnesium and I thought the standard enthalpy of formation for MgO would be equivalent. Is this true and if not what is the heat of combustion of magnesium (preferably per mole)?

Explanation / Answer

The enthalpy of formation of MgO is given as the elemental states being formed

Mg --> Mg(s)

O --> O2(g)

Then

2Mg(s) + O2(g) --> 2MgO(s)

NOTE that the Hf = -601.6 kJ/mol of MgO

therefore

Mg(s) + 1/2O2(g) --> MgO(s) H= -601.6 kJ/mol

now, by definition the H of combustion is

Mg(s) + O2(g) ---> X

in this case, X = MgO

then

Mg(s) + 1/2O2(g) ---> MgO(s)

you can assume Hrxn = Hcombustion!

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