Answer :
The enthalpy change (ΔH) for the reaction [tex]2 S (s) + 3 O_2 (g) → 2 SO_3[/tex] (g) is calculated as -792.2 kJ using Hess's Law which states that enthalpy change is same irrespective of the path.
In this problem, we are using the concept of Hess's Law, which is a significant concept in thermochemical calculations in chemistry. According to Hess's Law, the enthalpy change (ΔH) for a reaction is the same whether it takes place in one step or several steps. Therefore, we can calculate ΔH for the reaction [tex]2 S (s) + 3 O_2 (g) → 2 SO_3[/tex] (g) by adding the ΔH of the given reactions that add up to this reaction.
The first given reaction is: [tex]S (s) + O_2 (g) → SO_2[/tex](g) ΔH = -297.0 kJ. But we require 2 S (s), hence we multiply this equation by 2: [tex]2 S (s) + 2 O_2 (g) → 2 SO_2[/tex](g) ΔH = -2*(-297.0) = -594.0 kJ
The second given reaction is: [tex]2 SO_2(g) + O_2 (g) → 2 SO_3[/tex](g) ΔH = -198.2 kJ. These two equations on adding give us: [tex]2 S (s) + 3 O_2 (g) → 2 SO_3(g)[/tex], and adding the ΔH gives: ΔH = -594.0 kJ -198.2 kJ = -792.2 kJ
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