The standard heat of formation, in kcal/mol of Ba^2+ is :[Given : standard heat of formation of SO_4^2- ion (aq) = -216 kcal/mol, standard heat of crystallisation of BaSO_4(s) = -4.5 kcal/mol, standard heat of formation of BaSO_4(s) = -349 kcal/mol]

1. -128.5

2. -133.0

3. +133.0

4. +220.5

Doubtly Asked 30 Oct 2026 NEET UG 2025 Practice test neet Save WhatsApp Report

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Answer: 1. -128.5

Key idea: \(\mathrm{Ba^{2+}(aq)+SO_4^{2-}(aq)\to BaSO_4(s)}\) has \(\Delta H=-4.5\) kcal (crystallisation).

\(\Delta H_f(\mathrm{BaSO_4})=\Delta H_f(\mathrm{Ba^{2+}})+\Delta H_f(\mathrm{SO_4^{2-}})+(-4.5)\).
\(-349=x-216-4.5\).
\(x=-349+220.5=-128.5\) kcal/mol.

Option (1).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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