Calculate delta_f H for (s) from the following data: ZnS(s) - Zn(s) + S (rhombic), δ H_1 = 44 kcal/mol; 2ZnS(s) + 3(g) - 2ZnO(s) + 2(g), δ H_2 = -221.88 kcal/mol; 2(g) + (g) - 2(g), δ H_3 = -46.88

Question

Calculate delta_f H for $ZnSO_4$(s) from the following data: ZnS(s) -> Zn(s) + S (rhombic), δ H_1 = 44 kcal/mol; 2ZnS(s) + 3$O_2$(g) -> 2ZnO(s) + 2$SO_2$(g), δ H_2 = -221.88 kcal/mol; 2$SO_2$(g) + $O_2$(g) -> 2$SO_3$(g), δ H_3 = -46.88 kcal/mol; $ZnSO_4$(s) -> ZnO(s) + $SO_3$(g), δ H_4 = 55.1 kcal/mol

Prashant Kotian · Accepted Answer

Correct answer: A. We want Zn(s) + S(rhombic) + 2(g) -> (s). Sum the following: (1) Zn(s) + S(rhombic) -> ZnS(s) [δ H = -44 kcal]. (2) ZnS(s) + 1.5 (g) -> ZnO(s) + (g) [δ H = -110.94 kcal]. (3) (g) + 0.5 (g) -> (g) [δ H = -23.44 kcal]. (4) ZnO(s) + (g) -> (s) [δ H = -55.1 kcal]. Summing these yields the target equation. Thus, delta_f H = -44 - 110.94 - 23.44 - 55.1 = -233.48 kcal/mol.

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