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

## The reaction is: $\text{Mg"(s) + 1/2 "O"_2(g) -> "MgO} \left(s\right)$

Mar 2, 2015

The standard enthalpy change of formation, or $\Delta {H}_{f}^{\circ}$, 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, ${25}^{\circ} \text{C}$ and $\text{1 atm}$.

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

$\Delta {H}_{f}^{\circ} = \text{-601.6 kJ/mol}$.

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.