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Per NCERT §5.4(d) (thermochemical equations), if a chemical equation is REVERSED, what happens to Δ_r H°?
AIts sign is reversed (e.g. forward −91.8 → reverse +91.8 kJ/mol for NH₃ formation/decomposition)
BMultiplied by 2
CAlways becomes zero
DSign unchanged
Answer & Solution
Correct answer: A. Its sign is reversed (e.g. forward −91.8 → reverse +91.8 kJ/mol for NH₃ formation/decomposition)
Per NCERT §5.4(d) convention 3, reversing the equation reverses the sign of ΔH. Forward N₂+3H₂→2NH₃ is −91.8; reverse +91.8 kJ/mol.
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