A student needs to calculate the standard enthalpy of formation of magnesium oxide, MgO, using Hess's Law. The student has access to the following reactions and their corresponding enthalpy changes:1. Mg(s) + 1/2O2(g) → MgO(s) ΔH = -601.8 kJ/mol2. Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) ΔH = -450.7 kJ/mol3. H2(g) + 1/2O2(g) → H2O(l) ΔH = -285.8 kJ/molWhat is the standard enthalpy of formation of MgO from its elements?

Question

A student needs to calculate the standard enthalpy of formation of magnesium oxide, MgO, using Hess's Law. The student has access to the following reactions and their corresponding enthalpy changes:1. Mg(s) + 1/2O2(g) → MgO(s)   ΔH = -601.8 kJ/mol2. Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)   ΔH = -450.7 kJ/mol3. H2(g) + 1/2O2(g) → H2O(l)   ΔH = -285.8 kJ/molWhat is the standard enthalpy of formation of MgO from its elem

Answer 1

The standard enthalpy of formation of MgO from its elements is already given in the first reaction:Mg s  + 1/2O2 g   MgO s    H = -601.8 kJ/molThis reaction represents the formation of one mole of MgO from its elements, magnesium  Mg  and oxygen  O2 , in their standard states. Therefore, the standard enthalpy of formation of MgO is -601.8 kJ/mol.