Consider the following reaction and its corresponding enthalpy:
2 Mg (s) + O₂ (g) →2 MgO (s) D H ° _rxn= - 1204 kJ/mol What amount of heat is exchanged when 5.00 grams of magnesium metal reacts at constant pressure?

Question

Quizplus · Accepted Answer

The molar mass of Mg is 24.31 g/mol. 5.00 g of Mg is 5.00 g / 24.31 g/mol = 0.2057 mol. The reaction releases 1204 kJ for 2 mol of Mg, so for 0.2057 mol, the heat exchanged is (1204 kJ / 2 mol) * 0.2057 mol = -124 kJ.

Consider the Following Reaction and Its Corresponding Enthalpy