Chemistry - Thermochemistry Question with Solution | TestHub
The enthalpy of formation of KCl(s) from the following data is
(i) KOH(aq) + HCl(aq) → KCl(aq) + H2O(l); ΔH = -13.7 kcal
(ii) H2(g) + 1/2O2(g) → H2O(l); ΔH = -68.4 kcal
(iii) 1/2H2(g) + 1/2Cl2(g) + aq → HCl(aq); ΔH = -39.3 kcal
(iv) K(s) + 1/2O2(g) + 1/2H2(g) + aq → KOH(aq); ΔH = -116.5 kcal
(v) KCl(s) + aq → KCl(aq); ΔH = +4.4 kcal
Options:
Answer:
Solution:
The target reaction is K(s) + 1/2Cl2(g) tarrow KCl(s). To achieve this, we perform the following operations on the given reactions: add (iv), (iii), and (i), then reverse (ii) and reverse (v). The species KOH(aq), HCl(aq), KCl(aq), H2O, H2, O2, and aq will cancel out, leaving the target reaction.
The enthalpy change (Δ H) for the target reaction is calculated as follows:
Δ H = -116.5 - 39.3 - 13.7 - (-68.4) - (+4.4) = -105.5 kcal/mol
This corresponds to option (b).
