NEET2025Chemistry-Thermochemistry

NEET 2025 Chemistry Heat of Formation MCQ Question

Type: MCQ-numerical-Hard-Class 11

The standard heat of formation, in kcal/mol of Ba²⁺ is: [Given: standard heat of formation of SO₄²⁻ ion (aq) = -216 kcal/mol, standard heat of crystallisation of BaSO₄(s) = -4.5 kcal/mol, standard heat of formation of BaSO₄(s) = -349 kcal/mol]

A

-128.5

B

-133.0

C

+133.0

D

+220.5

Correct Answer

Option A

Detailed Explanation

Using the equation: ΔHf(Ba²⁺) = ΔHf(BaSO₄) - ΔHf(SO₄²⁻) - ΔHcryst(BaSO₄), we find ΔHf(Ba²⁺) = -³⁴⁹⁻ (-216) - (-4.5) = -133.0 kcal/mol.

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