Question
Calculate ΔfH for ZnSO4(s) from the following data
ZnS(s) → Zn(s) + S (rhombic), ΔH1 = 44 kcal/mol
2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g), ΔH2 = −221.88 kcal/mol
2SO2(g) + O2(g) → 2SO3(g), ΔH3 = −46.88 kcal/mol
ZnSO4(s) → ZnO(s) + SO3(g), ΔH4 = 55.1 kcal/mol
Options
Solution
Given thermo chemical equations are:
(a) $ZnS(s) \rightarrow Zn(s) + S(s);\Delta H = 44\text{kcal}$
(b) $2ZnS(s) + 3O_{3}(g) \rightarrow 2ZnO(s) + 2SO_{2}(g);\Delta H = 221.88\text{ kcal}$
(c) $2SO_{2}(g) + O_{2}(g) \rightarrow 2SO_{3}(g);\Delta H = 46.88\text{ kcal}$
(d) $ZnSO_{4}(s) \rightarrow ZnO(s) + SO_{3}(g);\Delta H = 55.1\text{ kcal}$
Required thermochemical equation is
$Zn(s) + S(s) + 2O_{2}(g) \rightarrow ZnSO_{4}(s);\Delta H = ? $$${\text{From }\frac{1}{2}(b) + \frac{1}{2}(c) - (a) - (d); }{\Delta H = \frac{1}{2}( - 221.88) + \frac{1}{2}( - 46.88) - (44) - (55.1) = - 233.48\text{ kcal}}$$
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