When 2 mol of solid magnesium (Mg) combines with 1 mole of oxygen gas (O2), 2 mol of solid magnesium oxide (MgO) is formed and 1204kJ of heat is released. Write the thermochemical equation for this combustion reaction.

Answer 1

2MgO + O2 ==> 2MgO delta H = -1204 kJ.
becomes
MgO + 1/2 O2 ==> MgO delta H = -602 kJ/mol for the thermochemical equation.

Answer 2

The question asks about the element magnesium reacting with oxygen gas, to form magnesium oxide. The solutions above show magnesium oxide reacting with oxygen gas to form magnesium oxide, which is incorrect.

Mg(s) + 1/2 O2(g) ====> MgO(s) delta H = -602 kJ/mole Mg(s)
2Mg(s) + O2(g) ======> 2MgO(s) delta H = -1204 kJ/mole O2(g)