Magnesium burns in oxygen to form magnesium oxide:

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

2\,\mathrm{Mg(s)} + \mathrm{O_2(g)} \rightarrow 2\,\mathrm{MgO(s)}

. The standard enthalpy of formation of

\mathrm{MgO(s)}

-601\,\text{kJ mol}^{-1}

; the standard enthalpies of formation of the elements in their reference states are zero. If

5.00\,\text{g}

of magnesium are burned completely under standard conditions, what is the enthalpy change for the reaction? (a)

-2.48 \times 10^{2}\,\text{kJ}

(b)

+1.24 \times 10^{2}\,\text{kJ}

(c)

-1.24 \times 10^{2}\,\text{kJ}

(d)

-6.02 \times 10^{2}\,\text{kJ}