Question

Use Table 8.3 to obtain \(\Delta H^{\circ}\) for the following thermochemical equations: (a) \(\mathrm{Mg}(\mathrm{OH})_{2}(s)+2 \mathrm{NH}_{4}^{+}(a q) \longrightarrow \mathrm{Mg}^{2+}(a q)+2 \mathrm{NH}_{3}(g)+\) \(2 \mathrm{H}_{2} \mathrm{O}(l)\) (b) \(\mathrm{PbO}(s)+\mathrm{C}(s) \longrightarrow \mathrm{CO}(g)+\mathrm{Pb}(s)\) (c) \(\mathrm{Mn}(s)+4 \mathrm{H}^{+}(a q)+\mathrm{SO}_{4}^{2-}(a q) \longrightarrow \mathrm{Mn}^{2+}(a q)+\mathrm{SO}_{2}(g)+$$2 \mathrm{H}_{2} \mathrm{O}(l)\)

Short answer

Question: Calculate the standard enthalpy change (∆H°) for the following reactions using the standard enthalpies of formation provided in Table 8.3: (a) Mg(OH)₂ + 2 NH₄⁺ → Mg²⁺ + 2 NH₃ + 2 H₂O (b) PbO + C → CO + Pb (c) Mn + 4 H⁺ + SO₄²⁻ → Mn²⁺ + SO₂ + 2 H₂O Please provide your answer in kJ/mol.

Step-by-step solution

(a) Calculate \(\Delta H^{\circ}\) for the reaction of Mg(OH)\(_2\) and NH\(_4^+\) ions

To calculate the standard enthalpy change for the reaction, use the formula mentioned above and refer to table 8.3 for standard enthalpies of formation. \(\Delta H^{\circ} = [(1\times\Delta H^{\circ}_{f, Mg^{2+}}) + (2\times\Delta H^{\circ}_{f, NH_3}) + (2\times\Delta H^{\circ}_{f, H_2O})] - [(1\times\Delta H^{\circ}_{f, Mg(OH)_2}) + (2\times\Delta H^{\circ}_{f, NH_4^+})]\) After filling in the values from the table, calculate the final \(\Delta H^{\circ}\)

(b) Calculate \(\Delta H^{\circ}\) for the reaction of PbO and C

Again, use the standard enthalpy change formula and refer to table 8.3 for standard enthalpies of formation. \(\Delta H^{\circ} = [(1\times\Delta H^{\circ}_{f, CO}) + (1\times\Delta H^{\circ}_{f, Pb})] - [(1\times\Delta H^{\circ}_{f, PbO}) + (1\times\Delta H^{\circ}_{f, C})]\) After filling in the values from the table, calculate the final \(\Delta H^{\circ}\)

(c) Calculate \(\Delta H^{\circ}\) for the reaction of Mn and H\(^+\) and SO\(_4^{2-}\) ions

Use the standard enthalpy change formula and refer to table 8.3 for standard enthalpies of formation as before. \(\Delta H^{\circ} = [(1\times\Delta H^{\circ}_{f, Mn^{2+}}) + (1\times\Delta H^{\circ}_{f, SO_2}) + (2\times\Delta H^{\circ}_{f, H_2O})] - [(1\times\Delta H^{\circ}_{f, Mn}) + (4\times\Delta H^{\circ}_{f, H^+}) + (1\times\Delta H^{\circ}_{f, SO_4^{2-}})]\) After filling in the values from the table, calculate the final \(\Delta H^{\circ}\)