# Given....2Mg(s) + O_2(g) rarr 2MgO(s) ; DeltaH_"rxn"=-1203*kJ*mol^-1 What enthalpy is associated with the combustion of FOUR moles of magnesium metal?

Jun 12, 2017

$\Delta H = - 2406 \cdot k J \ldots \ldots \ldots . .$
$2 M g \left(s\right) + {O}_{2} \left(g\right) \rightarrow 2 M g O \left(s\right)$ $\Delta {H}_{\text{rxn}} = - 1203 \cdot k J \cdot m o {l}^{-} 1$
Enthalpy terms are written per mole of reaction as written. We combust 4 moles of magnesium metal, and should therefore generate $2 \times - 1203 \cdot k J = - 2406 \cdot k J$.
Note that given these data we could write $\Delta {H}_{f}^{\circ} \left(M g O\right) = - 601.5 \cdot k J$. Why?