Question

What is the standard change in enthalpy of formation of `"MgO"(s)`?

The reaction is:

`"Mg"(s) + 1/2 "O"_2(g) -> "MgO"(s)`

Answer 1

The standard enthalpy change of formation, or `DeltaH_f^@`, of magnesium oxide will be -601.6 kJ/mol.

Explanation:

The reaction you're using represents the formation of magnesium oxide from its elements in their most stable forms at standard state, `25^@"C"` and `"1 atm"`.

In the case of formation reactions, the standard enthalpy change of formation for a compound is measured, not calculated; usually, you'll find this value listed either in books or online.

http://en.wikipedia.org/wiki/Standard_enthalpy_change_of_formation_%28data_table%29

So, in your case, the standard enthalpy change of formation for magnesium oxide was measured to be

`DeltaH_f^@ = "-601.6 kJ/mol"`.

In every day language, the large negative value indicates that this process releases quite a bit of energy as can be observed in the video below.